JP2011011326A - Tool and method for calibrating tool position of robot - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tool and a method for calibrating tool position for achieving the coincidence of the TCPs (tool center point) in three attitudes of the robot at one same point irrespective of the skill of an operator.SOLUTION: A tool coordinate system having a representative point of a tool 2 attached to the finger of a robot as the origin P is calibrated. A spherical tool 12 having a spherical surface 13 with a constant radius from the center A and a positioning tool 14 coming in contact with the spherical surface 13 to position the center A of the spherical surface 13 at a predetermined position B are prepared. The spherical tool 12 is attached to the tool 2 so that the representative point P of the tool 2 coincides with the center A. The positioning tool 14 is fixed at a predetermined position. The spherical surface 13 of the spherical tool 12 comes in contact with the positioning tool 14 to position the center A of the spherical tool 12 at the position B of the positioning tool 14 while the tool 2 is held in three or more attitudes. The relative position of the representative point P of the tool in the tool coordinate system is determined based on the position-attitude data of a reference point on a face plate in a robot coordinate system in each of the three or more attitudes of the tool 2.

Description

  The present invention relates to a tool position calibration jig and method for a robot in an automatic production system using a robot.

  FIG. 1 is an explanatory diagram showing a conventional general method. In this figure, (A) shows the appearance of the robot and the tool, (B) shows the relationship between the robot coordinate system and the tool coordinate system, and (C) shows the tool position calibration jig.

As shown in FIG. 1A, when the robot 1 is applied to various operations in an automatic production system, an end effector 2 such as a hand (hereinafter simply referred to as a “tool”) is a hand portion of a robot (such as a robot arm). Is attached to a robot tip plate 3 (hereinafter simply referred to as “face plate”) provided at the tip of the robot.
In this figure, point O is the origin of the robot coordinate system, point F is a representative point on the face plate, and point P is a tool center point (TCP), which is the origin of the tool coordinate system.

In order to cause the robot 1 to perform a predetermined work, the position and posture of the tool 2 are taught to the robot 1 by setting a tool coordinate system with the TCP (point P) as the origin. In general, the setting data of the tool coordinate system is the control of the robot as data representing a matrix / vector describing the relative position and posture of the tool coordinate system viewed from the representative point F (usually the center point) on the face plate 3. Given to the device.
Therefore, it is necessary to provide data representing the position and orientation of TCP (point P) with respect to the representative point F on the face plate 3. Hereinafter, this data is referred to as “tool parameter”.

In FIG. 1B, a point F1 is a representative point F on the face plate in an arbitrary posture of the robot.
In this case, since the vector (O → P) is the sum of the vector (O → F1) and the vector (F1 → P), the following equation (1) is established.
P _O = F1 _O + R _F × P _F (1)
Here, P _O is the position matrix of the robot coordinate system of the point P, F1 _O position matrix of the robot coordinate system of the point F1, R _F is homogeneous transformation matrix for transforming the tool coordinate system to the robot coordinate system, P _F is It is a position matrix of the tool coordinate system of the point P.

In the equation (1), the matrix R _F is determined by the configuration of the robot, and is a known transformation matrix that can be set alone without a tool before calibration of the tool coordinate system. The matrix F1 _O is a representative point F on the face plate in the robot coordinate system, and is also a known matrix before the calibration of the tool coordinate system.
Thus, the right side of the equation (1), only the matrix _{P F} is unknown. Here, P _F is the position matrix of the tool coordinate system of the point P, represented by three variables. These three variables correspond to the tool parameters described above.

  The tool parameters do not change even if the robot posture changes. Therefore, in the conventional general method, as shown in FIG. 1 (C), the robot 1 is placed in three or more postures so that the specific point of the tool desired to be set as TCP coincides with the same point P in the space. The position data in the robot coordinate system of the reference points F1, F2, and F3 on the face plate in each posture is acquired, and the relative position (tool parameter) in the TCP tool coordinate system is obtained based on this.

That is, in FIG. 1B, when F2 _O is the position matrix of the robot coordinate system of the point F2, and F3 _O is the position matrix of the robot coordinate system of the point F3, Expression (2) is established in the same manner as Expression (1). .
P _O = _F 1 _O + R _F × P _F = _F 2 _O + R _F × P _F = _F 3 _O + R _F × P _F (2)

Here, the matrices F2 _O and F3 _O are representative points on the face plate in the robot coordinate system, and are known before the calibration of the tool coordinate system, like the matrix F1 _O.
Accordingly, the unknown is only the matrix P _F (three parameters of the tool parameter), and three variables of the tool parameter can be obtained from the equation (2).

Patent documents 1 to 3 have already been disclosed in relation to the tool position calibration means of the robot.
Patent Documents 1 and 2 calibrate using a jig or the like. It is also known to set by numerical input based on drawing information or the like. Furthermore, Patent Document 3 performs calibration and setting by recognizing a specific point from data captured using a visual sensor or the like.

Japanese Patent Laid-Open No. 61-025206, “Robot Tool Position Setting Method” Japanese Patent Laid-Open No. 61-025207, “Tool Coordinate System Setting Method” Japanese Patent No. 4020994, “Robot Tool Coordinate System Correction Setting Method and End Effector Used in the Method”

The conventional means described above has the following problems.
In general, since the coincidence with the same point P in space is visually confirmed, the accuracy essentially depends on the visual observation. In the case where TCP is set at the tip of a pointed tool as shown in FIG. 1C, it is relatively easy to execute, but in the case of a tool where it is difficult to determine a specific point (TCP) on the tool, the robot It is difficult to match the TCP in the three postures to the same point. In addition, the operation for matching the same point is likely to have a difference in setting accuracy depending on the skill level of the operator, and since it is visually matched, the work is performed in a place very close to the tool, and there is a high risk of contact.

  As in Patent Documents 1 and 2, even when calibration is performed using a jig or the like, since the alignment is made with the naked eye, work is performed near the tool, and there is a high risk of contact.

  When setting by numerical input based on drawing information or the like, if the number of parts constituting the tool is large, there may be a case where the required accuracy cannot be ensured due to the accumulated error of each part. On the other hand, in order to increase the accuracy, it is necessary to increase the processing accuracy of each part, which increases the cost. In addition, the dimensions of the drawings and actual dimensions are often different for tools manufactured on site.

  Since Patent Document 3 uses a visual sensor or the like, the system becomes expensive although it does not depend on the skill level of the operator. In addition, when a camera or the like is used as a sensor, it cannot be used because it is easily affected by ambient light. Furthermore, environmental and operational constraints are likely to appear, such as requiring optical expertise for operation.

  In addition to the initial setting, once the tool coordinate system is set, the relative position and posture of the tool with respect to the robot hand origin may change due to a robot interference accident or the like. In particular, if a sensor or the like is interposed between the robot hand and the tool as an adapter, the adapter will be replaced due to a failure / damage or the sensor itself being changed / replaced, resulting in a shift in the position and orientation of the tool. Inevitable. The following A to C are conceivable as a countermeasure against such a situation.

A Re-adjust the tool mounting position and posture precisely to accurately reproduce the original tool position and posture (before the position and posture deviation occurred).
B Teach again so that the tool that caused the position and posture deviation can be used as it is.
C Set and reset (reset) the tool coordinate system to compensate for tool position and orientation deviations.

Method A requires skill and time for the adjustment work itself, and the burden on the worker is large. Also, depending on the type of tool, reproduction becomes very difficult. In the method B, the time required for the work becomes enormous, for example, when there are many taught programs.
In view of the above, there is a need for a technique that is inexpensive as the method C and that can be quickly implemented without depending on the skill level of the operator.

  The present invention has been devised to meet the above-described needs. In other words, an object of the present invention is to enable TCP to be used in three postures of a robot at low cost and easily with high accuracy without depending on the skill level of the operator, which can work at a remote place where there is no possibility of touching the tool. It is intended to provide a tool position calibration jig and method for a robot that can match the same point with each other and can determine the relative position of the tool representative point in the tool coordinate system.

According to the present invention, there is provided a robot tool position calibration jig for calibrating a tool coordinate system in which a representative point of a tool attached to a hand portion of the robot is an origin P,
A spherical jig having a spherical surface attached to one of the tool or a predetermined fixed position and having the representative point P as a center A;
A tool for calibrating the tool position of the robot, comprising: a positioning jig which is attached to the other of the tool or the predetermined fixed position and contacts the spherical surface and positions the center A of the spherical surface at the predetermined fixed position B. Tools are provided.

  According to an embodiment of the present invention, the positioning jig has an inverted conical or inverted prefix conical concave hole that contacts the spherical surface.

  According to another embodiment of the present invention, the positioning jig includes a plurality of spheres or cylindrical rollers arranged on the circumference at intervals.

According to the present invention, there is also provided a robot tool position calibration method for calibrating a tool coordinate system in which a representative point of a tool attached to the hand portion of the robot is an origin P,
(A) preparing a spherical jig having a spherical surface with a constant radius from the center A, and a positioning jig for contacting the spherical surface and positioning the center A at a predetermined fixed position B;
(B) One of the spherical jig and the positioning jig is attached to the tool so that the representative point P of the tool coincides with the center A or the fixed position B,
(C) fixing the other of the spherical jig and the positioning jig at a predetermined fixing position;
(D) While holding the tool in three or more postures, the spherical surface of the spherical jig is brought into contact with the positioning jig, and the center A of the spherical jig is positioned at the fixed position B of the positioning jig,
(E) A tool position calibration method for a robot is provided, wherein a relative position in a tool coordinate system of a tool representative point is obtained based on position data in a robot coordinate system of a reference point on a face plate in each posture. .

According to an embodiment of the present invention, the robot is force controllable,
In (D), the tool is moved so that the center A of the spherical jig is directed to the fixed position B of the positioning jig, and at the same time, the movement resistance in the plane perpendicular to the movement direction is force-controlled to zero, Positioning is performed at a position where the pressing force reaches a predetermined constant value.

  The above-described tool position calibration jig of the present invention includes a spherical jig and a positioning jig, the spherical jig has a spherical surface with the representative point P of the tool as a center A, and the positioning jig contacts the spherical surface. Thus, the center A of the spherical surface is positioned at a predetermined fixed position B.

For example, if a positioning jig having an inverted conical concave hole is fixed on the environment side and a spherical jig is fixed on the tool side, the center position of the spherical surface is obtained when the spherical surface is aligned with the inverted conical concave hole. A is located at a predetermined fixed position B of the positioning jig and does not change.
Therefore, when the center position A of this spherical surface is considered as the same point P in the space in the conventional method, the current position data of the robot is acquired in three or more postures while maintaining the state where the spherical surface is aligned with the concave hole. Thus, the relative position of the TCP to the face plate can be obtained by calculation.

  In addition, according to the tool position calibration method of the present invention using the above-described tool position calibration jig, (B) one of the spherical jig and the positioning jig, the representative point P of the tool is the center A or the fixed position B. (C) The other of the spherical jig and the positioning jig is fixed at a predetermined fixed position, and (D) while holding the tool in three or more postures (preferably a robot The spherical surface of the spherical jig is brought into contact with the positioning jig and the center A of the spherical jig is positioned at the fixed position B of the positioning jig. ) Can create a state where the spherical surface is combined.

Therefore, according to the apparatus and method of the present invention, it is possible to work at a remote place where there is no possibility of touching the tool, and it is inexpensive and easily performed with high accuracy without depending on the skill level of the operator. The TCP in the three postures can be matched with the same point, and the relative position of the tool representative point in the tool coordinate system can be obtained from this.

It is explanatory drawing which shows the conventional general method. It is a 1st embodiment figure of a tool position calibration jig by the present invention. It is a figure which shows the use condition of the tool position calibration jig | tool of FIG. It is a schematic diagram which shows the tool position calibration method of this invention. It is a flowchart which shows the tool position calibration method of this invention. It is a 2nd embodiment figure of a tool position calibration jig by the present invention. It is a 3rd embodiment figure of a tool position calibration jig by the present invention.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the common part in each figure, and the overlapping description is abbreviate | omitted.

  FIG. 2 is a diagram showing a first embodiment of a tool position calibration jig according to the present invention. In this figure, (A) shows a force sensor and a tool, (B) shows a spherical jig of a tool position calibration jig, and (C) shows a positioning jig of a tool position calibration jig.

In FIG. 2A, 2 is a tool, P is a TCP of the tool 2, 4 is a force sensor, and F is a representative point on the face plate 3. That is, the tool 2 to be calibrated is a gripper in this example, and is attached to the face plate 3 via the force sensor 4.
The force sensor 4 is generally used for force control of the robot, but the force sensor 4 is not essential as long as the robot can control the force. In this example, the representative point F on the face plate 3 is the center of the joint surface between the robot arm and the tool, but may be other than the center.

  As shown in FIGS. 2B and 2C, the tool position calibration jig 10 of the robot according to the present invention includes a spherical jig 12 and a positioning jig 14.

  In this example, the spherical jig 12 includes a spherical portion 12a having a spherical surface 13 having a constant radius R from the center A, and the spherical portion 12a so that the center A of the spherical surface 13 is positioned at the representative point P (TCP) of the tool 2. Is attached to the tool 2 (gripper). The spherical surface 13 may be a part of a sphere as long as it can contact the positioning jig 14 and position the center A of the spherical surface 13 at a predetermined fixed position B (described later).

The positioning jig 14 is attached to a predetermined fixed position (for example, an immovable position on the environment side) and contacts the spherical surface 13 of the spherical jig 12 to position the center A of the spherical surface 13 at a predetermined fixed position B.
In this example, the positioning jig 14 is a block having an inverted conical or inverted prefix conical recessed hole 15 that contacts the spherical surface 13. The apex angle of the inverted cone or inverted prefix cone is preferably 90 degrees, but is arbitrary as long as the inner surface of the concave hole 15 can contact the spherical surface 13.

  The spherical jig 12 and the positioning jig 14 may be interchanged between the tool side and the installation side. That is, the positioning jig 14 is attached to the tool 2 so that the fixed position B is located at the representative point P (TCP) of the tool 2, the spherical jig 12 is attached to a predetermined fixed position, and the concave hole of the positioning jig 14 The predetermined fixed position B may be positioned at the center A of the spherical surface 13 in contact with 15.

  The spherical jig 12 is attached to the tool 2 by the attachment portion 12b. The center A of the spherical surface 13 and the representative point P (TCP) of the tool 2 are preferably geometrically identical. As long as the relative position with respect to the point P is known, it does not have to coincide exactly.

FIG. 3 is a diagram illustrating a usage state of the tool position calibration jig of FIG. This figure shows the tool 2 (gripper) in FIG. 2A with the mounting portion 12b of the spherical jig 12 attached, and the tool is moved so that the spherical surface 13 of the spherical jig 12 is opposite to the positioning jig 14. The state which contacted the conical or reverse prefix conical concave hole 15 is shown.
In this state, the representative point P (TCP) of the tool 2 is located at the center A of the spherical surface 13, and the center A of the spherical surface 13 is located at a predetermined fixed position B of the positioning jig 14. That is, in this state, the representative point P of the tool 2, the center A of the spherical surface 13, and the predetermined fixed position B of the positioning jig 14 are all located at the same geometric position.

  FIG. 4 is a schematic diagram showing the tool position calibration method of the present invention. In this figure, (A) is the movement state of the tool while maintaining the posture of the tool, (B) is the state where the spherical surface of the spherical jig is pressed against the positioning jig, and (C) is the center A of the spherical jig. Is positioned at a fixed position B of the positioning jig.

  FIG. 5 is a flowchart showing the tool position calibration method of the present invention. Hereinafter, the method of the present invention will be described with reference to FIGS.

The method of the present invention comprises the following steps (processes) (A) to (E).
In the step (A), the above-described spherical jig 12 having the spherical surface 13 having a constant radius R from the center A, and the above-described positioning jig 14 for contacting the spherical surface 13 and positioning the center A at a predetermined fixed position B. And prepare.
In step (B), one of the spherical jig 12 and the positioning jig 14 (in this example, the spherical jig 12) is arranged such that the representative point P of the tool 2 coincides with the center A or the fixed position B (in this example, the center A). Attach to the tool 2 as shown.
In step (C), the other of the spherical jig 12 and the positioning jig 14 (in this example, the positioning jig 14) is fixed at a predetermined fixing position.
In step (D), while holding the tool 2 in three or more postures, the spherical surface 13 of the spherical jig 12 is brought into contact with the positioning jig 14 so that the center A of the spherical jig 12 is positioned at the fixed position of the positioning jig 14. Position to B.
In step (E), the relative position of the tool representative point in the tool coordinate system is obtained based on the position / posture (direction) data in the robot coordinate system of the reference point on the face plate in each posture.

The flowchart of FIG. 5 shows the (D) step and the (E) step in detail. In this example, it is assumed that the robot 2 is configured to be capable of force control.
The flowchart in FIG. 5 includes steps (steps) S1 to S8.
In step S1, the center A of the spherical jig 12 is moved so as to be substantially above the fixed position B of the positioning jig 14.
Next, in step S2, the tool 2 is held in a posture of 3 or more. These three or more postures are arbitrary as long as they are different from each other.
Next, in step S3, the tool 2 is moved with the center A of the spherical jig 12 facing the fixed position B of the positioning jig 14 (FIG. 4A), and the movement resistance in the plane orthogonal to the moving direction is reduced. The force is controlled to zero (FIG. 4B), and in step S4, the force is stopped at a position where the pressing force in the moving direction has reached a predetermined constant value (FIG. 4C).

  At this stop position, the position and orientation (direction) data of the reference point on the face plate in the robot coordinate system is acquired in step S5, the hand is raised in step S6, and the data in three or more orientations is obtained in step S7. If (D) is acquired, step (D) is terminated.

  After acquiring data in three or more postures, in step (E) and S8, TCP position calibration calculation is performed, and the tool coordinates of the tool representative point based on the position data in the robot coordinate system of the reference point on the face plate in each posture Find the relative position in the system.

FIG. 6 is a diagram showing a second embodiment of the tool position calibration jig according to the present invention. In this figure, (A) is a figure which shows the use condition of a tool position calibration jig | tool, (B) is a figure which shows the use condition of a tool.
In this example, the robot is a deburring robot and the tool 2 is a combination of a spindle 5 and a collet 6. The spherical portion 12 a of the spherical jig 12 has a spherical shape, and the mounting portion 12 b is configured so that the tip center P of the tool 7 and the center A of the spherical surface 13 coincide with the collet 6.
Other configurations are the same as those in the first embodiment.

FIG. 7 is a diagram showing a third embodiment of the tool position calibration jig according to the present invention. In this example, the spherical jig 12 is the same as that of the first embodiment, but the positioning jig 14 has a plurality of spheres 16 (or cylindrical rollers) arranged at intervals on the circumference.
Other configurations are the same as those in the first embodiment.

  The above-described tool position calibration jig 10 of the present invention has a spherical jig 12 and a positioning jig 14, and the spherical jig 12 has a spherical surface 13 with the representative point P of the tool 2 as the center A. The tool 14 comes into contact with the spherical surface 13 to position the center A of the spherical surface 13 at a predetermined fixed position B.

For example, when the positioning jig 14 having the inverted conical concave hole 15 is fixed to the environment side and the spherical jig 12 is fixed to the tool side, the spherical surface 13 is aligned with the inverted conical concave hole 15. Then, the center position A of the spherical surface 13 is located at a predetermined fixed position B of the positioning jig 14 and does not change.
Therefore, when the center position A of the spherical surface 13 is considered as the same point P in the space in the conventional method, the face of the robot 1 in the current robot coordinate system is maintained in a state where the spherical surface is aligned with the concave hole 15. By acquiring three or more positions and position (orientation) data of the reference point on the plate, the relative position of the TCP to the face plate can be calculated.

  Further, according to the tool position calibration method of the present invention using the above-described tool position calibration jig 10, (B) one of the spherical jig 12 and the positioning jig 14 is set so that the representative point P of the tool 2 is the center A. Alternatively, it is attached to the tool 2 so as to coincide with the fixed position B, (C) the other of the spherical jig 12 and the positioning jig 14 is fixed at a predetermined fixing position, and (D) the tool 2 is held in three or more postures. However, since the spherical surface of the spherical jig is brought into contact with the positioning jig (preferably by force control of the robot) and the center A of the spherical jig is positioned at the fixed position B of the positioning jig, the positioning jig can be easily It is possible to create a state in which the spherical surface is combined with the (conical concave hole).

  Therefore, according to the apparatus and method of the present invention, it is possible to work at a remote place where there is no possibility of contact with the tool 2, and without depending on the skill level of the operator, the robot can be easily and inexpensively with high accuracy. The TCP in the three postures can be made coincident with the same point, and the relative position of the tool representative point in the tool coordinate system can be obtained from this.

Therefore, according to the apparatus and method of the present invention, the following effects can be obtained.
(1) The tool coordinate system calibration of the robot can be performed without variations in accuracy due to the skill level of the operator.
(2) Calibration can be performed in a short time. Even if a change occurs due to a robot interference accident, it can be quickly recovered.
(3) It is possible to reduce the risk of adjustment by manual adjustment close to the robot while visually observing.
(4) If the TCP approximate position is known, it can be automated by incorporating it into the robot controller. Self-checking for tool position and posture deviation is also possible.
(5) In recent years, robots for applications such as assembly, deburring, and machining are often configured so that force control is possible. In such a case, high-precision calibration can be performed at low cost.

  In addition, this invention is not limited to embodiment mentioned above, Of course, a various change can be added in the range which does not deviate from the summary of this invention.

1 robot, 2 tools (end effector),
3 Face plate (robot tip plate),
4 Force sensor,
5 spindles, 6 collets, 7 tools,
10 Tool position calibration jig, 12 Spherical jig,
12a ball part, 12b mounting part,
13 spherical surface, 14 positioning jig,
15 concave hole

Claims (5)

A tool position calibration jig for a robot for calibrating a tool coordinate system in which a representative point of a tool attached to a hand portion of the robot is an origin P,
A spherical jig having a spherical surface attached to one of the tool or a predetermined fixed position and having the representative point P as a center A;
A tool for calibrating the tool position of the robot, comprising: a positioning jig which is attached to the other of the tool or the predetermined fixed position and contacts the spherical surface and positions the center A of the spherical surface at the predetermined fixed position B. Ingredients.   The tool positioning calibration jig according to claim 1, wherein the positioning jig has an inverted conical or inverted prefix conical concave hole that contacts the spherical surface.   2. The tool position calibration jig for a robot according to claim 1, wherein the positioning jig includes a plurality of spheres or cylindrical rollers arranged on the circumference at intervals. 3. A method for calibrating a tool position of a robot for calibrating a tool coordinate system having a representative point of a tool attached to a hand portion of the robot as an origin P,
(A) preparing a spherical jig having a spherical surface with a constant radius from the center A, and a positioning jig for contacting the spherical surface and positioning the center A at a predetermined fixed position B;
(B) One of the spherical jig and the positioning jig is attached to the tool so that the representative point P of the tool coincides with the center A or the fixed position B,
(C) fixing the other of the spherical jig and the positioning jig at a predetermined fixing position;
(D) While holding the tool in three or more postures, the spherical surface of the spherical jig is brought into contact with the positioning jig, and the center A of the spherical jig is positioned at the fixed position B of the positioning jig,
(E) A tool position calibration of a robot, characterized in that a relative position in a tool coordinate system of a tool representative point is obtained based on position / posture (direction) data in a robot coordinate system of a reference point on the face plate in each posture. Method. The robot is force controllable,
In (D), the tool is moved so that the center A of the spherical jig is directed to the fixed position B of the positioning jig, and at the same time, the movement resistance in the plane perpendicular to the movement direction is force-controlled to zero, 5. The robot tool position calibration method according to claim 4, wherein positioning is performed at a position where the pressing force reaches a predetermined constant value.

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