CN115136198A

CN115136198A - Coordinate system calibration method, teaching board and protruding part

Info

Publication number: CN115136198A
Application number: CN202080096265.XA
Authority: CN
Inventors: 梁栋
Original assignee: Siemens Ltd China
Current assignee: Siemens Ltd China
Priority date: 2020-02-14
Filing date: 2020-02-14
Publication date: 2022-09-30
Also published as: WO2021159489A1

Abstract

A coordinate system calibration method, apparatus and computer readable medium. A coordinate calibration method includes: keeping the z axis of an actuator (20) of a mechanical arm (21) vertical to a workbench (40), moving the mechanical arm (21) to enable a groove (71) of a teaching board (70) to be clamped with a protrusion (60) fixedly connected with the actuator (20), enabling the center point of the protrusion (60) to be overlapped with the origin of a coordinate system of the actuator (20), and enabling the center point of the protrusion (60) to be overlapped with the center point of the groove (71) during clamping; recording a first coordinate of the current position in a coordinate system of the actuator (20); moving the mechanical arm (21) for a certain distance along the z axis of the actuator (20) and in the direction away from the workbench (40), and controlling a camera (10) on the mechanical arm (21) to take a picture of the teaching board (70); calculating second coordinates of respective central points of at least two pictures (72) in the shot pictures under a coordinate system of the camera (10), wherein the central points of the at least two pictures (72) are different and different from the central point of the groove (71); and calibrating according to the coordinates of the central point of each picture in the coordinate system of the actuator (20) and the coordinate system of the camera (10).

Description

Coordinate system calibration method, teaching board and protruding part

Technical Field

The invention relates to the technical field of industrial robots, in particular to a coordinate system calibration method, an demonstrating board and a protruding part.

Background

By "eye on hand" robot is meant that the camera (eye) is mounted on the actuator (hand, e.g. a gripper) to which the robot arm is attached, rather than being mounted beside the robot. In order to realize the mutual matching between the actuator and the camera in the automatic execution operation process of the actuator, the conversion relation between the coordinate system of the actuator and the coordinate system of the camera needs to be determined, namely, the hand-eye calibration is carried out.

Fig. 1 illustrates one method of hand-eye calibration currently in use. In this method, the user 30 controls the robot arm 21 to move along a set path through the teach pendant 50 and causes the actuator 20 to touch each point on the table 40, so as to acquire coordinates of the points in the actuator coordinate system. Then, the mechanical arm 21 is controlled to move to the photographing position and the camera 10 is controlled to photograph, so as to obtain the coordinates of the point touched by the mechanical arm 21 in the camera coordinate system.

In the existing hand-eye calibration method, in order to obtain the conversion relation between the coordinate system of the actuator and the coordinate system of the camera, the actuator of the mechanical arm needs to be controlled to touch a plurality of points, so that the actuator needs to move to each point for a plurality of times, and the operation is complex and time-consuming.

Disclosure of Invention

The embodiment of the invention provides a coordinate system calibration method, a teaching board and a protruding part, and provides a scheme with simple and convenient operation.

In a first aspect, a coordinate system calibration method is provided. The method can comprise the following steps: under the condition that the z axis of the mechanical arm actuator is kept vertical to the workbench, the following operations are executed;

-moving the robot arm to engage a groove of the teaching board with a projection fixedly connected to the actuator, the center point of the projection coinciding with the origin of the coordinate system of the actuator and, when engaged, the center point of the projection coinciding with the center point of the groove;

-recording a first coordinate of a current position in a coordinate system of the actuator;

-moving the robotic arm a distance along the z-axis of the actuator and away from the table;

-controlling a camera on the mechanical arm to take a picture of the teaching board;

-calculating second coordinates of respective center points of at least two pictures in the taken pictures under a coordinate system of the camera, wherein the center points of the at least two pictures are different from each other and from the center point of the groove;

-calculating a third coordinate of the center point of each of the at least two pictures in the coordinate system of the actuator according to the position relationship between the center point of each of the at least two pictures and the center point of the groove and the first coordinate;

-determining a translation relationship between the coordinate system of the actuator and the coordinate system of the camera from the respective third coordinates and the respective second coordinates.

In a second aspect, there is provided a teaching board for coordinate system calibration, the teaching board being positionable on a table of a robotic arm, comprising:

-a groove, wherein the groove is snappable with a protrusion to which the robot arm is fixedly connected;

-at least two pictures, wherein the center points of the at least two pictures are different from each other and from the center point of the groove.

In a third aspect, a protrusion for coordinate system calibration is provided, the protrusion being fixedly connected to an actuator of a robotic arm; the projection may engage a groove on one of the teaching boards.

In a fourth aspect, a coordinate system calibration apparatus is provided, which includes at least one processor and at least one memory, coupled to the at least one processor, configured to perform the method of the first aspect.

In a fifth aspect, there is provided a computer-readable medium for coordinate system calibration, having stored thereon computer-executable instructions, that when executed, cause at least one processor to perform the method of the first aspect.

The projection is fixedly connected with the actuator, and the origin of the coordinate system of the actuator is determined by clamping the projection with the groove on the teaching board; on the other hand, the actuator is moved along the z-axis, and the coordinates of the central point of each picture in the camera coordinate system are obtained by photographing, so that the relationship between the two coordinate systems is determined. The teaching board and the actuator are matched in position only once, so that the operation difficulty is reduced. Through the arrangement of the clamping mode, the accuracy of the relative position relation is ensured, and the accuracy of the coordinate system calibration method is improved.

For any of the above aspects, optionally, the at least two pictures are different from each other, and when each second coordinate is calculated, the at least two pictures are identified in the shot pictures according to a pre-stored template, and the second coordinate of the center point of each identified picture in the coordinate system of the camera is calculated. Therefore, the calibration speed can be improved, and the operation is simple and convenient.

For any of the above aspects, optionally, the groove has two symmetry axes perpendicular to each other; the teaching board further comprises: and marks positioned around the groove and used for mutually distinguishing four quadrants divided by the two symmetrical axes. In this way, the camera can distinguish the direction of the teaching board.

For any of the above aspects, optionally, the groove has two symmetry axes perpendicular to each other; the at least two pictures are different and the number of the pictures is a multiple of four, the number of the pictures in each quadrant divided by the two symmetry axes is the same, and any picture has a picture symmetrical to the picture in the position in the adjacent quadrant. Thus, the coordinates of the central point of each picture in the coordinate system of the actuator can be conveniently calculated.

For any of the above aspects, the at least two pictures are both circular. Thus, the coordinates of the center point of each picture in the coordinate system of the actuator can be calculated more easily and accurately.

Drawings

Fig. 1 illustrates a method of hand-eye calibration.

Fig. 2 is a flowchart of a coordinate system calibration method according to an embodiment of the present invention.

Fig. 3 illustrates the conversion between the actuator coordinate system and the camera coordinate system in an embodiment of the present invention.

Fig. 4A to 4C illustrate an operation process of the coordinate system calibration method provided by the embodiment of the invention.

Fig. 5A and 5B illustrate an instructional board provided by an embodiment of the invention.

FIG. 6 illustrates a protrusion for coordinate system calibration provided by an embodiment of the present invention.

Fig. 7 shows the condition in which the projection is engaged with the groove.

Fig. 8 illustrates a coordinate system calibration apparatus provided by an embodiment of the present invention.

List of reference numerals:

Detailed Description

the subject matter described herein will now be discussed with reference to example embodiments. It should be understood that these embodiments are discussed only to enable those skilled in the art to better understand and thereby implement the subject matter described herein, and are not intended to limit the scope, applicability, or examples set forth in the claims. Changes may be made in the function and arrangement of elements discussed without departing from the scope of the disclosure. Various examples may omit, substitute, or add various procedures or components as needed. For example, the described methods may be performed in an order different from that described, and various steps may be added, omitted, or combined. In addition, features described with respect to some examples may also be combined in other examples.

As used herein, the term "include" and its variants mean open-ended terms, meaning "including but not limited to. The term "based on" means "based at least in part on". The terms "one embodiment" and "an embodiment" mean "at least one embodiment". The term "another embodiment" means "at least one other embodiment". The terms "first," "second," and the like may refer to different or the same object. Other definitions, whether explicit or implicit, may be included below. Unless the context clearly dictates otherwise, the definition of a term is consistent throughout the specification.

Next, a coordinate system calibration method 200 according to an embodiment of the present invention is described with reference to fig. 2, fig. 3, and fig. 4A to fig. 4C. The objective is to find the relationship between the coordinate system 81(x, y, z) of the actuator 20 and the coordinate system 82(x ', y ', z ') of the camera head 10 shown in fig. 3. The method presupposes that the z-axis of the coordinate system 81 of the actuator 20 coincides with or is parallel to the z' -axis of the coordinate system 82 of the camera 10. If an included angle exists between the z axis and the z' axis, the included angle needs to be calibrated in advance to be 0; or the angle can be taken into account and its effect removed during the calculation in the following steps. Thus, here the relationship between the two coordinate systems is determined, in fact the relationship between (x, y) and (x ', y').

As shown in fig. 2, the method may include the steps of:

with the z-axis of the actuator 20 of the robot arm 21 held perpendicular to the table 40,

s201: the robot arm 21 is moved closer to the table 40 so that the groove 71 of the teaching board 70 engages with the protrusion 60 fixedly attached to the actuator 20 (as shown in fig. 4B).

This step can be accomplished using a teach pendant. Referring to fig. 4A, the robot arm 21 may be moved to the center of the table 40, and the vertical distance from the table 40 may be as small as possible, but a space for the teaching board 70 to move is reserved. The table 40 can be placed horizontally, vertically, or at an angle with respect to the horizontal direction, as long as the plane of the table 40 is perpendicular to the z-axis of the coordinate system 81 of the actuator 20, which may be determined according to engineering practice.

The movement of the robot arm 21 toward the teaching board 70 on the table 40 may also be coordinated with the movement of the teaching board 70 to facilitate the engagement of the protrusions 60 with the grooves 71 on the teaching board 70.

The center point of the protrusion 60 coincides with the origin of the coordinate system 81 of the actuator 20, and when the protrusion 60 and the recess 71 are engaged with each other, the center point coincides with the center point of the recess.

The protrusion 60 needs to be fixedly connected to the actuator 20, that is, the relative position relationship between the protrusion 60 and the actuator 20 does not change, so that after the protrusion 60 is engaged with the groove 71 on the teaching board 70, accurate coordinates of the actuator 20 in the coordinate system can be found. Fixed connections include, but are not limited to, adhesive bonding, bolting (as shown in fig. 6), magnetic attraction, and the like. Alternatively, the control actuator 20 picks up and grasps the protrusion 60 before step S201 is executed.

S202: recording a first coordinate of the current position in a coordinate system of the actuator 20;

since the center point of the protrusion 60 coincides with the origin of the coordinate system 81 of the actuator 20, and when engaged, the center point of the protrusion 60 coincides with the center point of the groove 71. Therefore, the first coordinate is regarded as the origin of the coordinate system 81 of the actuator 20. This first coordinate serves as a reference for the subsequent calculation of the relationship between the coordinate system 81 of the actuator 20 and the coordinate system 82 of the camera head 10.

S203: moving the robotic arm 21 a distance along the z-axis of the actuator 20 and away from the table 40;

s204: controlling the camera 10 on the mechanical arm 21 to take a picture of the teaching board 70 (as shown in fig. 4C);

s205: calculating second coordinates of respective central points of at least two pictures 72 in the shot pictures under a coordinate system of the camera 10, wherein the central points of the at least two pictures are different and different from the central point of the groove 71;

here, it is mentioned that at least two pictures 72 are required because the conversion of the relationship between the two coordinate systems requires the coordinates of at least two points in the two coordinate systems, respectively. In practice, there may be three pictures, four, five, six, etc., and the more pictures, the more coordinates of the acquired points, and the more accurate the result of the coordinate system calibration.

S206: calculating a third coordinate of the central point of each of the at least two pictures 72 in the coordinate system of the actuator 20 according to the position relationship between the central point of each of the at least two pictures 72 and the central point of the groove 71 and the first coordinate;

when the actuator 20 is engaged, the coordinates of the center point of the groove 71 are the coordinates of the origin of the coordinate system 81 of the actuator 20, and the positional relationship of the center point of each picture 72 on the teaching board 70 with respect to the center point of the groove 71 is known, so that the coordinates of the center point of each picture 72 in the coordinate system 81 of the actuator 20, i.e., "the third coordinates", can be calculated based on the coordinates.

S207: and determining the conversion relation between the coordinate system of the actuator 20 and the coordinate system of the camera 10 according to the third coordinates and the second coordinates.

Since there are coordinates of the center point of each picture 72 in the coordinate system 81 of the actuator 20 and in the coordinate system 82 of the camera 10, the relationship between the two coordinate systems can be obtained accordingly. Alternatively, a least squares method (least square) may be used to calculate a rotation matrix (rotaion matrix) of the coordinate system.

In the above-described flow, on the one hand, the projection 60 is fixedly connected to the actuator 20, and the origin of the coordinate system 81 of the actuator 20 is determined by engaging the projection 60 with the groove 71 of the teaching board 70; on the other hand, the actuator 20 is moved along the z-axis, and the coordinates of the center point of each picture 72 in the coordinate system of the camera 10 are obtained by photographing, so that the relationship between the two coordinate systems is determined. In the above process, the teaching board 70 and the actuator 20 are only required to be matched in position once, which is convenient to use as shown in fig. 1, and the operation difficulty is greatly reduced. Through the arrangement of the clamping mode, the accuracy of the relative position relation is ensured, and the accuracy of the coordinate system calibration method is improved.

Alternatively, the at least two pictures 72 may be identified in the captured pictures according to a pre-stored template, and the second coordinates of the center point of each identified picture in the coordinate system of the camera 10 may be calculated, so that the calibration speed may be increased, and the operation is simple.

As shown in fig. 5A and 5B, the respective pictures 72 are different, and preferably, the respective pictures 72 may be designed to have a large difference therebetween for easy recognition. For example, in fig. 5A, a different picture 72 is designed by combining a long bar with an origin; for another example, in fig. 5A, the upper row and the lower row are designed as a one-digit picture and a two-digit picture, respectively, so that the upper row and the lower row are easily distinguished. On the other hand, in order to find the center point of each picture 72, the picture 72 may be designed to be circular. While the groove 71 and the protrusion 60 may be designed to be symmetrical, such as: the recess 71 is shaped with two axes of symmetry perpendicular to each other and correspondingly the protrusion 60 has two axes of symmetry perpendicular to each other, which facilitates finding the central point. Further, as shown in fig. 5A, 5B and 6, the shape of the groove 71 and the protrusion 60 may be designed as a cross, wherein one axis of symmetry is long and the other axis of symmetry is short, and the long axis of symmetry is in the x-axis or y-axis direction of the coordinate system 81 of the actuator 20 and the short axis of symmetry is in the other direction of the x-axis and y-axis of the coordinate system 81 of the actuator 20. Thus, if the engagement between the protrusion 60 and the groove 71 is to be achieved on the flat surface of the table 40, only a single rotation angle is available, and the failure of the calibration due to the improper operation does not occur.

Further, if the groove 71 in the teaching board 70 has two symmetry axes perpendicular to each other, optionally, the teaching board 70 may further include marks 73 around the groove 71 to distinguish four quadrants divided by the two symmetry axes from each other (as shown in fig. 5A and 5B). This may enable the camera head 10 to distinguish the orientation of the teaching board 70.

In addition, if the groove 71 in the teaching board 70 has two symmetry axes perpendicular to each other, optionally, the at least two pictures 72 are different and are in a multiple of four, the number of the pictures in each quadrant divided by the two symmetry axes is the same, and any picture has a picture symmetrical to its position in an adjacent quadrant. This facilitates the calculation of the coordinates of the center point of each picture in the coordinate system 81 of the actuator 20.

In which, whether the mark 73 or each picture 72, the pattern may be composed of different shapes and colors for easy identification.

As shown in fig. 8, an embodiment of the present invention further provides a coordinate system calibration apparatus 10, including:

a robot arm control module 101 configured to perform the aforementioned steps S201, S203;

a calculation module 102 configured to perform the aforementioned steps S202, S205, S206 and S207;

the camera control module 103 is configured to execute the aforementioned step S204.

Alternatively, these modules may be stored in the at least one memory 105 as program modules in the coordinate system calibration program 80, which when invoked by the at least one processor 104 performs the aforementioned steps S201-S207.

Optionally, the at least one memory 105 may also pre-store a template 90 for picture recognition, which is used to recognize the picture 72 from the captured picture in the aforementioned step S205.

In the device architecture shown in fig. 8, the at least one memory 105, the at least one processor 104, and the optional I/O interface may communicate with each other via a bus.

The modules 101 to 103 may also be regarded as functional modules implemented by hardware, and are used to implement various functions involved in the coordinate system calibration method executed by the coordinate system calibration apparatus 10, for example, control logics of various processes involved in the method are pre-burned into a chip such as a Field-Programmable Gate Array (FPGA) chip or a Complex Programmable Logic Device (CPLD), and the chip or the Device executes the functions of the modules, and the specific implementation manner may be determined according to engineering practice.

Furthermore, an embodiment of the present invention further provides a computer readable medium, which stores computer readable instructions, and when the computer readable instructions are executed by a processor, the processor is caused to execute the aforementioned coordinate system calibration method. Examples of the computer-readable medium include floppy disks, hard disks, magneto-optical disks, optical disks (e.g., CD-ROMs, CD-R, CD-RWs, DVD-ROMs, DVD-RAMs, DVD-RWs, DVD + RWs), magnetic tapes, nonvolatile memory cards, and ROMs. Alternatively, the computer readable instructions may be downloaded from a server computer or from a cloud over a communications network.

It should be noted that not all steps and modules in the above flows and system structure diagrams are necessary, and some steps or modules may be omitted according to actual needs. The execution sequence of the steps is not fixed and can be adjusted according to the needs. The system structure described in the above embodiments may be a physical structure or a logical structure, that is, some modules may be implemented by the same physical entity, or some modules may be implemented by a plurality of physical entities, or some components in a plurality of independent devices may be implemented together.

Claims

A coordinate system calibration method (200), comprising: under the condition that the z axis of an actuator (20) of a mechanical arm (21) is kept vertical to a workbench (40), the following operations are executed;

-moving (S201) the robot arm (21) to engage a groove (71) of the teaching board (70) with a protrusion (60) fixedly connected to the actuator (20), the center point of the protrusion (60) coinciding with the origin of the coordinate system of the actuator (20) and the center point of the protrusion (60) coinciding with the center point of the groove (71) upon engagement;

-recording (S202) a first coordinate of a current position in a coordinate system of the actuator (20);

-moving (S203) the robot arm (21) a distance along the z-axis of the actuator (20) and away from the table (40);

-controlling (S204) a camera (10) on the robotic arm (21) to take a picture of the teaching board (70);

-calculating (S205) second coordinates of the respective center points of at least two pictures (72) in the taken picture in the coordinate system of the camera (10), wherein the center points of the at least two pictures are different from each other and from the center point of the groove;

-calculating (S206) third coordinates of the respective center points of the at least two pictures (72) in the coordinate system of the actuator (20) according to the first coordinates and the positional relationship between the respective center points of the at least two pictures (72) and the center point of the groove (71);

-determining (S207) a transformation between the coordinate system of the actuator (20) and the coordinate system of the camera (10) from the respective third coordinates and the respective second coordinates.
The method according to claim 1, wherein said at least two pictures (72) are different from each other, calculating (S205) each of said second coordinates, comprising:

-identifying said at least two pictures (72) among the pictures taken according to a pre-stored template (90), and calculating second coordinates of the central point of each identified picture in the coordinate system of the camera (10).
Teaching board (70) for coordinate system calibration, said teaching board (70) being positionable on a table (40) of a robotic arm (21), comprising:

-a groove (71), wherein the groove (71) is snappable with a protrusion (60) to which the robot arm (21) is fixedly connected;

-at least two pictures (72), wherein the center points of the at least two pictures are different from each other and from the center point of the groove.
The teaching board (70) of claim 3,

-said groove (71) has two axes of symmetry perpendicular to each other;

-the teaching board (70) further comprising: marks (73) located around the groove (71) to distinguish four quadrants divided by the two axes of symmetry from each other.
The teaching board (70) of claim 3,

-said groove (71) has two axes of symmetry perpendicular to each other;

-said at least two pictures (72) are different and are in a number of multiples of four, the number of pictures in each quadrant divided by said two axes of symmetry being the same, and any picture has a picture symmetrical in its position in the adjacent quadrant.
The teaching board (70) according to any of claims 3-5, wherein the teaching board (70) is adapted to perform the method according to claim 1 or 2.
Projection (60) for coordinate system calibration, characterized in that,

-said projection (60) is fixedly connected to an actuator (20) of a robot arm (21);

-said projection (60) being engageable with a recess (71) in a teaching board (70).
The projection (60) of claim 7,

-the protrusion (60) is used for performing the method according to claim 1 or 2.
Coordinate system calibration device (10), characterized in that it comprises means for performing the method according to claim 1 or 2.
Coordinate system calibration device (10), characterized in that it comprises:

-at least one processor (104);

-at least one memory (105), coupled with the at least one processor (104), configured to perform the method according to claim 1 or 2.
A computer-readable medium for coordinate system calibration, having stored thereon computer-executable instructions that, when executed, cause at least one processor to perform the method of claim 1 or 2.
The device according to any one of claims 1 to 11, wherein the at least two pictures (72) are circular.