CN111028298A

CN111028298A - Convergent binocular system for rigid coordinate system space transformation calibration

Info

Publication number: CN111028298A
Application number: CN201911304061.6A
Authority: CN
Inventors: 李长乐; 张雷锋; 张学贺; 范逸伦; 赵杰
Original assignee: Harbin Institute of Technology Shenzhen
Current assignee: Harbin Institute of Technology Shenzhen
Priority date: 2019-12-17
Filing date: 2019-12-17
Publication date: 2020-04-17
Anticipated expiration: 2039-12-17
Also published as: CN111028298B

Abstract

A convergent binocular system for rigid coordinate system space transformation calibration belongs to the technical field of rigid coordinate system space transformation positioning. The invention solves the problems of slow calibration speed and poor accuracy of the existing tool with poor rigidity when the calibration is carried out by the spatial transformation of the calibration system. The invention mainly adopts a convergent binocular system, two cameras are placed in an optical axis intersection mode, the size of an intersected visual space can be flexibly changed by adjusting the relative pose of the two cameras so as to adapt to the size and calibration resolution requirements of different rigid bodies, a camera space coordinate system is established through a related camera calibration technology, the camera space coordinate of any point placed in the intersected visual measurement space can be accurately represented through a certain image processing algorithm, and the pose of a key point coordinate system related to a rigid body in a known coordinate system can be established by controlling the rigid body to perform certain steps of translational motion and rotational motion. The invention is suitable for calibrating the position posture of the rigid body.

Description

Convergent binocular system for rigid coordinate system space transformation calibration

Technical Field

The invention belongs to the technical field of rigid coordinate system space transformation positioning, and particularly relates to a convergent binocular system for rigid coordinate system space transformation calibration.

Background

The rigid body coordinate system space transformation is the basis of rigid body kinematics, in the field of robots, whether the rigid body coordinate system space transformation is accurate or not directly affects the working performance of the robot, and because the design size is inconsistent with the actual size due to errors of mechanical manufacturing and assembly, the robot must be calibrated kinematically before being put into use. In the field of surgical robot navigation, infrared optical navigation is the most common technology, but an infrared optical navigation system can only accurately track a standard tool provided by a manufacturer generally, so that the standard tool is usually fixedly connected to an actually used tool in the using process, for the tool with a simple shape and good rigidity, some manufacturers provide a convenient and quick principal point rotation calibration method to realize accurate conversion between a standard tool coordinate system and an actually used tool key point coordinate system, but for the tool with a complex shape and poor rigidity, the problems of low calibration speed and poor accuracy still exist.

Disclosure of Invention

The invention aims to solve the problems of low calibration speed and poor accuracy when the existing tool with poor rigidity is used for calibrating the spatial transformation of a calibration system. A convergent binocular system for rigid coordinate system space transformation calibration is provided.

The invention relates to a convergent binocular system for rigid coordinate system space transformation calibration, which comprises a camera a1, two plane light sources 2, two light source fixing plates 3, a cross adjusting table a, a cross adjusting table b, a camera b5, a base 8 and an upper computer 9, wherein the camera a1 is arranged on the upper surface of the rigid coordinate system;

the cross-shaped adjusting table a comprises a longitudinal sliding table a10 and a transverse sliding table a 11; the transverse sliding table a11 is arranged on the upper side of the longitudinal sliding table a10, and the sliding direction of the transverse sliding table a11 is perpendicular to that of the longitudinal sliding table a 10;

the cross-shaped adjusting table b comprises a transverse sliding table b6 and a longitudinal sliding table b 7; the transverse sliding table b6 is arranged on the longitudinal sliding table b7, and the sliding direction of the transverse sliding table b6 is perpendicular to that of the longitudinal sliding table b 7;

the cross adjusting table a, the cross adjusting table b and the two light source fixing plates 3 are fixed on the upper surface of the base 8 to form a vision measuring space; the vision measurement space is used for placing a rigid body to be calibrated;

the sliding direction of the longitudinal sliding table a10 is vertical to that of the longitudinal sliding table b 7;

the sliding direction of the transverse sliding table a11 is vertical to that of the transverse sliding table b 6;

the two light source fixing plates 3 are adjacently arranged, and the two light source fixing plates 3 are both fixed with a plane light source 2;

the sliding directions of the longitudinal sliding table a10 and the longitudinal sliding table b7 are respectively perpendicular to the two light source fixing plates 3;

a camera a1 is fixed on the transverse sliding table a11, and a shooting surface of the camera a1 is opposite to a plane light source;

a camera b5 is fixed on the transverse sliding table b6, and the shooting surface of the camera b5 is opposite to the other plane light source; the camera b5 and the camera a1 are used for acquiring images of rigid bodies to be calibrated in the vision measurement space;

the camera b5 and the camera a1 respectively upload the acquired images of the rigid body to be calibrated to the upper computer 9;

four motors are adopted to correspondingly control the transverse sliding table b6, the longitudinal sliding table b7, the longitudinal sliding table a10 and the transverse sliding table a11 one by one;

the upper computer 9 is used for performing rapid three-dimensional shape matching on the image of the rigid body 4 to be calibrated, calculating the coordinates of the key points to be calibrated in the visual measurement space, acquiring the coordinates of a plurality of groups of key points in the visual measurement space and the coordinates of a certain determined point of the plurality of groups of rigid bodies in an external known coordinate system by using pictures of different poses of the rigid bodies, further acquiring the corresponding relation between the visual measurement space and the external known coordinate system, and calculating the positions of the key points associated with the rigid body to be calibrated in the external known coordinate system.

Further, the upper computer 9 is further configured to determine a ratio of the pixel area of the rigid body image to be calibrated to the total width, and when the ratio is not within the ratio threshold interval, send a control signal to one or more of the four motors to control one or more of the longitudinal sliding table a10, the longitudinal sliding table b7, the transverse sliding table b6, or the longitudinal sliding table b7 to move until the ratio of the pixel area of the rigid body image to be calibrated to the total width is within the ratio threshold interval.

Further, the proportion threshold interval of the pixel area of the rigid body image to be calibrated accounting for the whole breadth is 30% -50%.

Furthermore, the control signal input ends of the four motors are respectively connected with the upper computer 9 through data lines;

the upper computer 9 is further configured to determine whether the rigid body 4 to be calibrated is complete in the image, and when the rigid body 4 to be calibrated is incomplete in the image, send a control signal to one or more of the four motors respectively to control one or more of the longitudinal sliding table a10, the longitudinal sliding table b7, the transverse sliding table b6, or the longitudinal sliding table b7 to move until a complete rigid body image to be calibrated is obtained.

The convergent binocular system for rigid body coordinate system space transformation calibration, disclosed by the invention, can quickly and accurately calibrate the pose of the key point coordinate system associated with the rigid body in the known coordinate system. The invention mainly adopts a convergent binocular system, two cameras are placed in an optical axis intersection mode, the size of an intersected visual space can be flexibly changed by adjusting the relative pose of the two cameras so as to adapt to the size and calibration resolution requirements of different rigid bodies, a camera space coordinate system is established through a related camera calibration technology, the camera space coordinate of any point placed in the intersected visual measurement space can be accurately represented through a certain image processing algorithm, and the pose (position pose) of a key point coordinate system associated with a rigid body in a known coordinate system can be established by controlling the rigid body to perform certain steps of translational motion and rotational motion. The invention has the advantages of high sensitivity, adjustable measuring space, strong usability, wide application range and the like, effectively reduces the cost of the calibration process, and improves the calibration efficiency and the calibration precision.

Drawings

FIG. 1 is a schematic structural diagram of a convergent binocular system for rigid coordinate system spatial transformation calibration according to the present invention;

fig. 2 to 4 are schematic diagrams of adjusting the position of the camera a or the camera b to visually measure the spatial position and the size change; wherein,

FIG. 2 is a schematic diagram of the spatial position and size of the visual measurement when the distances between the camera a and the camera b are equal to the rigid body to be calibrated;

FIG. 3 is a schematic diagram of the spatial position and size of the visual measurement when the distance between the camera a and the rigid body to be calibrated is greater than the distance between the camera b and the rigid body to be calibrated;

fig. 4 is a schematic diagram of the spatial position and size of the visual measurement when the distance between the camera a and the rigid body to be calibrated is smaller than the distance between the camera b and the rigid body to be calibrated.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.

The invention is further described with reference to the following drawings and specific examples, which are not intended to be limiting.

The first embodiment is as follows: the following describes the present embodiment with reference to fig. 1 and fig. 2, and the present embodiment describes a convergent binocular system for rigid coordinate system space transformation calibration, which includes a camera a1, two planar light sources 2, two light source fixing plates 3, a cross adjustment table a, a cross adjustment table b, a camera b5, a base 8 and an upper computer 9;

the upper computer 9 is used for rapidly matching the three-dimensional shape of the image of the rigid body 4 to be calibrated, calculating the coordinates of the key points to be calibrated in the visual measurement space, acquiring the coordinates of a plurality of groups of key points in the visual measurement space and the coordinates of a certain determined point of the plurality of groups of rigid bodies in an external known coordinate system by using pictures of different poses of the rigid bodies, further acquiring the corresponding relation between the visual measurement space and the external known coordinate system, and calculating the positions of the key points associated with the rigid body to be calibrated in the external known coordinate system.

The upper computer of the invention comprises an image processing module, the image processing module processes the received image of the rigid body to be calibrated, firstly, the positions of two cameras are flexibly adjusted according to the sizes of the shot image and the rigid body to be calibrated to adapt to the rigid bodies to be calibrated with different shapes and sizes, and simultaneously, only image comparison is needed when judging whether the acquired rigid body to be calibrated is complete, the principle is shown in figures 2 to 4, in order to simplify analysis, if the two cameras are horizontally arranged, only the positioning problem of space points at a pixel level is considered, the size of the space point corresponding to a single pixel is formed by intersecting rays of the boundaries of the single pixel sent out by the optical centers of the two cameras, only a single row of pixels (similar multiple rows of pixels) are analyzed, the intersecting part of the pixels is in the shape of a quadrangle, namely the resolution, because the resolutions of each point in a measuring space are different, the resolution of the pixel at the optical center is related to the resolution, when the resolution is adjusted, the camera a moves rightwards, the whole measuring space is reduced and moves towards the direction close to the camera b, the resolution is improved, and meanwhile, the measuring space is long and narrow and is suitable for a rigid body with a long and narrow shape; the two cameras approach to each other along the optical center direction of the other camera at the same time, the whole measuring space is greatly reduced, the resolution is further improved, and the method is suitable for occasions with small rigid bodies to be measured but high precision.

Obviously, the method has lower resolution for a larger rigid body to be calibrated, calculates the proportion of pixel area of a camera shooting breadth under each posture of the rigid body to be calibrated by analyzing an image, ensures that the proportion is more than 30% below 50% so as to ensure that the rigid body to be calibrated has enough motion space and certain measurement precision, controls a motor to be far away from the rigid body to be calibrated when the proportion is more than 50%, controls the motor to be close to the rigid body to be calibrated when the proportion is less than 30%, then calibrates internal reference and external reference of the system, finally carries out rapid matching of three-dimensional shape by using a three-dimensional vision system consisting of two cameras, calculates the coordinate of a key point to be calibrated in the three-dimensional vision system, executes certain motion through the rigid body so as to obtain the corresponding relation between the coordinate of a plurality of groups of key points in the three-dimensional vision system and the pose of a certain determined point on the, and calculating the pose of the key point coordinate system associated with the rigid body to be calibrated in an external known coordinate system.

In the using process, firstly, the rigid body 4 to be calibrated is placed into a visual measurement space (namely a space where two camera shooting spaces are intersected), the transverse sliding table b6, the longitudinal sliding table b7, the longitudinal sliding table a10 and the transverse sliding table a11 are respectively adjusted to enable the rigid body 4 to be calibrated to be located at a proper position in the visual measurement space, the rigid body 4 to be calibrated is externally controlled to move to all poses required by calibration in the visual measurement space, the rigid body 4 to be calibrated is shot through the camera a1 and the camera b5 and data are transmitted to the upper computer 9, pictures of all the shot poses are processed through an image processing algorithm, and the pose of a key point coordinate system associated with the rigid body 4 to be calibrated in an external known coordinate system is calculated.

Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that features described in different dependent claims and herein may be combined in ways different from those described in the original claims. It is also to be understood that features described in connection with individual embodiments may be used in other described embodiments.

Claims

1. A convergent binocular system for spatial transformation and calibration of a rigid body coordinate system, characterized in that the system comprises a camera a (1), two plane light sources (2), two light source fixing plates (3), a cross Adjustment table a, cross adjustment table b, camera b (5), base (8) and upper computer (9);

The cross adjustment table a includes a longitudinal sliding table a (10) and a transverse sliding table a (11); the transverse sliding table a (11) is arranged on the upper side of the longitudinal sliding table a (10), and the transverse sliding table a (11) The sliding direction of is perpendicular to the sliding direction of the longitudinal sliding table a (10);

The cross adjustment table b includes a transverse sliding table b(6) and a longitudinal sliding table b(7); the transverse sliding table b(6) is arranged on the longitudinal sliding table b(7), and the sliding table b(6) slides The direction is perpendicular to the sliding direction of the longitudinal sliding table b(7);

The cross adjustment table a, the cross adjustment table b and the two light source fixing plates (3) are all fixed on the upper surface of the base (8) to form a visual measurement space; the visual measurement space is used for placing the rigid body to be calibrated;

The sliding direction of the longitudinal sliding table a (10) is perpendicular to the sliding direction of the longitudinal sliding table b (7);

The sliding direction of the lateral slide a (11) is perpendicular to the sliding direction of the lateral slide b (6);

Two light source fixing plates (3) are arranged adjacently, and the two light source fixing plates (3) are both fixed with a plane light source (2);

The sliding directions of the longitudinal sliding table a (10) and the longitudinal sliding table b (7) are respectively perpendicular to the two light source fixing plates (3);

A camera a (1) is fixed on the lateral slide a (11), and the shooting surface of the camera a (1) is opposite to a plane light source;

A camera b(5) is fixed on the lateral sliding table b(6), and the shooting surface of the camera b(5) is opposite to another plane light source; the camera b(5) and the camera a(1) are used for visual measurement of the space The rigid body to be calibrated is used for image acquisition;

The camera b (5) and the camera a (1) respectively upload the collected images of the rigid body to be calibrated to the upper computer (9);

Four motors are used to control the transverse slide table b (6), the longitudinal slide table b (7), the longitudinal slide table a (10) and the transverse slide table a (11) in one-to-one correspondence;

The upper computer (9) is used to quickly match the three-dimensional shape of the image of the rigid body to be calibrated (4), calculate the coordinates of the key points to be calibrated in the visual measurement space, and use the pictures of different poses of the rigid body to obtain multiple sets of key points in the visual field. The coordinates of the measurement space and the coordinates of a certain point of multiple sets of rigid bodies in the external known coordinate system, and then the corresponding relationship between the visual measurement space and the external known coordinate system is obtained, and the key points associated with the rigid body to be calibrated are calculated. position in the coordinate system.

2. a kind of convergent binocular system for rigid body coordinate system space transformation calibration according to claim 1, is characterized in that, host computer (9) is also used for judging the ratio that the pixel area of rigid body image to be calibrated accounts for the whole width , when the ratio is not within the ratio threshold range, send control signals to one or more of the four motors to control the longitudinal slide a (10), the longitudinal slide b (7), and the lateral slide b (6) Or one or more of the vertical slides b(7) are moved until the ratio of the pixel area of the rigid body image to be calibrated to the entire frame is within the proportional threshold range.

3 . The convergent binocular system for spatial transformation and calibration of rigid body coordinate system according to claim 2 , wherein the pixel area of the rigid body image to be calibrated accounts for the proportion of the entire width of the image, and the threshold range is 30%-50%. 4 .

4. a kind of convergent binocular system for rigid body coordinate system space transformation calibration according to claim 1, is characterized in that, the control signal input end of four motors is respectively connected with host computer (9) by data line;

The host computer (9) is also used for judging whether the rigid body (4) to be calibrated is complete in the image, and when the rigid body (4) to be calibrated is incomplete in the image, it sends a control signal to one or more of the four motors, respectively, One or more of the longitudinal slide a (10), the longitudinal slide b (7), the lateral slide b (6) or the longitudinal slide b (7) are controlled to move until a complete image of the rigid body to be calibrated is obtained.