TWI891549B - A calibration method for robotic arm tool center point without a tool apex - Google Patents

Abstract

The present invention provides an innovative calibration method for robotic arm tool center point without a tool apex. The said calibration method successfully addresses the limitations of the conventional technologies that rely on physical tool tip recognition. The method integrates 2D vision sensors and contour sensors, successfully developing a technology capable of automatically calibrating the tool center point coordinates for tools without a defined tool apex.

Description

Calibration method for tool center of robot arm without tool tip point

A method for calibrating a tool of a robot arm, in particular a method for calibrating a tool without a tool tip of a robot arm.

Traditional manufacturing used to emphasize economies of scale, requiring high production volumes to reduce costs and increase profits. However, with shifting consumer patterns, consumers are gradually shifting from "buying what manufacturers sell" to "buying what I need and want." Consequently, the trend toward smaller quantities and a wider variety of products has spread across various industries. Furthermore, the rise of online information has fueled consumers' desire and anticipation for new things, shortening product lifecycles. For example, the automotive industry's trend of significantly shortening the lifecycle of new models reflects the manufacturing industry's shift from traditional, single-line, large-scale production to a model that prioritizes diversity and small batches. This shift has forced the industry to seek new solutions.

On the other hand, faced with an aging population and declining birthrates, labor-intensive manufacturing industries are facing challenges from labor shortages and rising costs. Furthermore, the retirement of experienced workers, coupled with the labor shortage facing the manufacturing industry, is making the transfer of experience and skills increasingly difficult. These changes in production processes have fueled advancements in robotic arm technology, expanding from simple tasks like loading and unloading to more complex processing stages.

To implement a robotic arm in precision-critical machining applications, not only does the robotic arm itself need to be calibrated, but the relative positions of various objects within the robotic arm's machining system must also be confirmed. For example, the precise coordinates of the tool center point (TCP) and the workpiece coordinate system (WOB coordinate) must be accurately determined. These coordinates typically require calibration. Traditional tool center calibration often relies on visual control of the robotic arm's motion, ensuring that the tool center reaches the same position in space with four different tool postures. However, manual calibration is time-consuming and subject to human error.

Most of the existing automatic calibration methods rely on the identification of the physical tool tip. Therefore, if the tool does not have a tool tip, the original tool must be replaced with a fixture with a sharp point (or a pointed rod) so that the tool center point of the pointed rod and the actual tool have the same position to meet the limitations of the calibration method. However, this method requires the actual tool to be replaced after calibration, and the disassembly and assembly action will cause additional assembly errors and is difficult to meet the accuracy requirements. Currently, only a few methods are available for calibrating the tool center point of a sharp point, and these methods have their limitations: existing methods require replacing the tool with a sensor, measuring the three-dimensional coordinates of a specified feature point using 3D measurement equipment, and then completing the calibration by geometrically estimating the relationship between the sensing point and the tool center point. Although this method does not require the use of a sharp rod, it still requires removing the sensor and reinstalling it on the actual application tool after calibration, which can introduce assembly errors.

To address the calibration issues associated with robotic arm tools without tool tip points, the present invention provides a method for calibrating the center of robotic arm tools without tool tip points. The method comprises the following steps: Step 1: Mounting a sphere of known radius on a flange surface of a robotic arm and using a vision sensor to obtain information about the sphere and calibrate the coordinates of the sphere's center relative to the flange surface of the robotic arm; Step 2: Using a contour sensor and the vision sensor to simultaneously obtain information about the sphere, and combining the information from the contour sensor and the vision sensor to calibrate the relative positional relationship between the robotic arm and the contour sensor; and Step 3: Finally, a tool required for the actual application is mounted on the flange surface of the robot arm. The vision sensor and the profile sensor are used to obtain tool information. Based on this information, corresponding control instructions are generated to move the tool to a specified position. This calibrates the tool axis and the tool center point, completing the calibration of the tool without a tool tip point.

In step 1, the image information of the visual sensor at two different viewing angles is used to control the movement of the robotic arm, ultimately causing the center of the sphere to reach the same position in space in four different postures, thereby obtaining the coordinates of the center of the sphere relative to the flange surface.

The center position of the sphere is corrected by using a rotating disk to change the viewing angle of the visual sensor. The robot arm is controlled to move at two different viewing angles, thereby causing the center of the sphere to reach the same position in space with different postures. Finally, the coordinates of the center of the sphere are obtained through kinematic equations.

In step 2, motion control is performed based on the information obtained by the contour sensor, and the relative relationship between the contour sensor coordinate system and the reference coordinate system of the robot arm is obtained to convert the command into a command relative to the reference coordinate system of the robot arm.

Before calibrating the relative position between the contour sensor and the robot arm, the coordinates of the center of the sphere mounted on the flange surface of the robot arm relative to the flange surface coordinate system are obtained.

Among them, the position calibration of the center of the sphere relative to the flange coordinate system is completed. After obtaining the coordinates, the contour sensor and the visual sensor are used to simultaneously obtain the sphere information to calibrate the position relationship between the robot arm and the contour sensor.

Among them, calibrating the contour sensor and the robot arm reference coordinate system includes controlling the robot arm to move the ball to a position where the contour sensor can capture the contour, and simultaneously obtaining the coordinates of the center of the ball relative to the robot arm reference coordinate system and the coordinates relative to the contour sensor coordinate system. The calibration is completed after obtaining several different positions.

After determining the conversion relationship between the contour sensor and the reference coordinate system of the robot arm, the tool coordinate system is calibrated.

From the above description, it can be seen that the present invention has the following beneficial effects and advantages:

1. The present invention's calibration method for a tool without a tool tip point primarily calibrates the tool-axis orientation and tool center point position. The proposed method utilizes a 2D profile sensor and a 2D vision sensor for calibration, both of which are mounted on a rotating disk. Before calibration, the precise relative relationship between the sensor and the robotic arm must be established. A sphere of known radius is mounted on the flange surface of the robotic arm. The sensor acquires information about the sphere and then calibrates the relative relationship between the sensor and the robotic arm. Finally, the tool required for the actual machining application (such as a grinding wheel) can be mounted on the robotic arm, and the sensor is used to obtain the tool-axis orientation and tool center point coordinates of the tool without a tool tip point.

2. This invention proposes an innovative method for calibrating tool centers in robotic arms without a tool tip point, successfully overcoming the limitations of existing technologies that rely on physical tool tip identification. By integrating a 2D vision sensor with a contour sensor, a technology has been developed that can automatically calibrate tool centers in robotic arms without a tool tip point. This calibration method overcomes challenges faced by traditional methods, such as the need to use a surrogate tip for calibration when the tool tip cannot be identified.

The present invention will be described and illustrated in detail below using several preferred embodiments. The attached figures are merely exemplary representations or embodiments of the present invention. For those with ordinary knowledge in the field to which the present invention belongs, the present invention can be applied to other similar situations based on these figures without making any further efforts.

The "system", "device", "unit" and/or "module" used in the present invention below is a method for distinguishing different components, elements, parts, parts or assemblies at different levels. However, if other words can achieve the same purpose, they can be replaced by other expressions. As shown in the present invention, unless the context clearly indicates an exception, the words "a", "an", "an" and/or "the" do not specifically refer to the singular and may also include the plural. Generally speaking, the terms "include" and "comprising" only indicate the inclusion of clearly identified steps and elements, and these steps and elements do not constitute an exclusive list. The method or apparatus may also include other steps or elements.

Flowcharts are used throughout this disclosure to illustrate the operations performed by the system according to embodiments of the present invention. It should be understood that the preceding and following operations do not necessarily need to be performed in exact order. Instead, the steps may be processed in reverse order or simultaneously. Similarly to the ball 10, other operations may be added to these processes, or one or more operations may be removed from these processes.

Please refer to Figures 1, 2 and 3, which are a flowchart and a schematic diagram of the method for calibrating the center of a tool without a tool tip of a robot arm of the present invention. The steps include:

Step S1: Mount a sphere 10 of known radius on a flange surface 21 of a robotic arm 20, and utilize a vision sensor 30 to obtain information about the sphere 10 and thereby calibrate the coordinates of a center 11 of the sphere 10 relative to the flange surface 21 of the robotic arm 20.

Step S2: Utilize a contour sensor 40 and the visual sensor 30 to simultaneously obtain information about the sphere 10, and combine the information from the contour sensor 40 and the visual sensor 30 to calibrate the relative position relationship between the robot arm 20 and the contour sensor 40; and

Step S3: Finally, a tool T required for the actual application is mounted on the flange surface 21 of the robot arm 20. The vision sensor 30 and the profile sensor 40 are used to obtain information about the tool T. Based on the obtained information, corresponding control instructions are generated to move the tool T to a specified position to calibrate the axial direction of the tool T and the center point position of the tool T. This completes the calibration of the tool T without a tool tip point.

In step S2, motion control is performed based on the contour sensing information, so the coordinate system of the contour sensor 40 must be obtained. and the reference coordinate system of the robot arm 20 The relative relationship between the command and the reference coordinate system of the robot arm 20 is converted into a command; the method for obtaining the conversion relationship provided by the present invention replaces the multiple sets of distance sensors in the existing technology with one visual sensor 30 to reduce the error caused by the difficulty of hardware assembly.

As shown in FIG2, 3A, 3B and 3C, the method provided by the present invention first obtains the coordinate system of the center 11 S ₀ of the sphere 10 mounted on the flange surface 21 of the robot arm 20 relative to the flange surface 21 before calibrating the relative relationship between the contour sensor 40 and the robot arm 20. The coordinates S _0F (not shown) of the image are calibrated as follows: (1) First, obtain the 2D coordinate system of the visual sensor 30 and the reference coordinate system of the robot arm 20 The orientation conversion relationship enables the motion command relative to the visual sensor 30 to be converted into a command relative to the reference coordinate system of the robot arm 20, wherein A rotating disk with an angle of 50 (2) controlling the movement of the robot arm 20 so that the sphere 10 reaches the same position in space in four different postures, and recording the combination of joint coordinates of the robot arm 20 when reaching the same position in space to obtain the coordinates of the center 11 of the sphere 10 relative to the flange surface 21.

In terms of position correction of the center 11 of the sphere 10, the present invention utilizes the rotating disk 50 to change the viewing angle of the visual sensor 30, and controls the movement of the robot arm 20 at two different viewing angles, thereby making the center 11 of the sphere 10 reach the same position in space with different postures. Finally, the coordinates of the center 11 of the sphere 10 can be obtained through the kinematic equation. The reference coordinate system of the visual sensor 30 The conversion relationship can be achieved by moving the ball 10 along and direction and obtain the coordinate system relative to the image sensor The vector is then used again and The transformation relationship can be obtained by the condition of being perpendicular to each other in space. The 20 coordinate system of the robot arm is obtained. The coordinate system of the visual sensor 30 The steps to convert the relationship are as follows:

The visual sensor 30 is mounted on the rotating disk 50 to form a sensing module, and then the sensing module is mounted within the motion range of the robotic arm 20 so that the ball 10 can move within the field of view of the visual sensor 30, as shown in FIG3A.

Rotate the rotating disk 50 to any angle and record the angle as Then, the ball 10 is moved to any position within the visual field of the visual sensor 30 as the starting point, and then The direction moves an arbitrary length and obtains the movement vector projected on the visual sensor 30. The corresponding space vector is .

Move the ball 10 to any position within the field of view as the starting point, and then The direction moves an arbitrary length and obtains the movement vector projected on the visual sensor 30. , and its corresponding space vector is .

Move the ball 10 to any position within the field of view as the starting point, and then The direction moves an arbitrary length and obtains the movement vector projected on the visual sensor 30. , and its corresponding space vector is .

use and The vertical characteristics in space are obtained by equations 1 to 3, as shown in FIG3B , where I in FIG3B indicates that the visual sensor 30 is at the first position.

= 0 …Equation 1.

= 0 …Equation 2.

= 0 …Equation 3.

Solving equations 1 to 3 yields:

…Equation 4.

…Formula 5.

…Equation 6.

From equations 4 to 6, we can see that the two solutions differ by a negative sign, so we can use the visual sensor to determine whether the ball 10 is moving along and When moving, the radius of the image of the sphere 10 changes, and the center of the sphere 11 is judged to be moving toward or away from the visual sensor to select the correct solution.

The reference coordinate system of the robot arm 20 and visual sensor coordinate system The conversion relationship is as follows:

…Formula 7.

in Along the visual sensor coordinate system Direction, The reference coordinate system along the robot arm 20 Direction, To convert a vector from the visual sensor coordinate system Convert to the reference coordinate system of the robot arm 20 Represents the rotation matrix.

Rotate the rotating disk 50 to any other angle:

If the rotating disk 50 rotates in the direction relative to Direction Known, the angle of the rotating disk is 50 Time coordinate system and the reference coordinate system of the robot arm 20 The coordinate transformation relationship is as follows: and The relationship is shown in FIG3C , where I in FIG3C indicates that the visual sensor 30 is at the first position, and II indicates that the visual sensor 30 is at the second position:

…Equation 8.

in, , , To convert the direction vector from the visual sensor coordinate system Convert to the reference coordinate system of the robot arm 20 Represents the rotation matrix.

If the rotating disk 50 rotates in the direction relative to If the direction is unknown, then follow the method from step 2 to step 6 to find and the reference coordinate system of the robot arm 20 The coordinate conversion relationship of the rotating disk 50 can be determined by the relationship of formula 8. Obtain:

…Formula 9.

…Equation 10.

…Equation 11.

Obtain The rotation matrix of the vector from the visual coordinate system to the reference coordinate system of the robot arm 20 can be obtained by using Equation 8 when the rotating disk 50 rotates to any position.

Please refer to FIG3A , in detail, in the aforementioned step S1, it is preferable to use the image information of the visual sensor 30 at two different viewing angles to control the movement of the robot arm 20, so that the center 11 of the sphere 10 reaches the same position in space in four different postures. , the coordinates of the center 11 of the sphere 10 relative to the flange surface 21 can be obtained. The four sets of postures should cover all directions within the tool working range as much as possible to ensure the accuracy of the calibration results. The process is as follows:

Move the robot arm 20 so that the center 11 of the sphere 10 Located within the field of view and as far away from the image boundary as possible to avoid the correction process from deviating beyond the field of view and failing to obtain the image to generate corresponding motion control commands.

Record the center of the ball 10 11 Respectively relative to the rotating disk 50 degrees and When the image coordinates of the visual sensor 30 ,make .

Generate azimuth increments through random number generator , and controls the robot arm 20 to change the posture of the ball 10 to a new azimuth If the new azimuth exceeds the range of motion, the center of the sphere 10 11 deviates from the field of view, or is close to the recorded tool posture and cannot include all directions of the tool working range, the azimuth increment is regenerated. Rotate the rotary disk 50 degrees to , using the visual sensor to obtain the image coordinates of the current sphere 10 and the center 11 , and calculate the direction of movement , and then use Equation 7 to convert S _c1 into , control the robot arm 20 along direction until the image coordinate of the sphere center 11 moves to _Os1 , as shown in FIG4A.

Rotate the rotary plate 50 degrees to , using the visual sensor to obtain the current image coordinates O _E2 of the center 11 of the sphere 10 and calculate the moving direction , and then use Equation 8 to convert S _c2 into , control the robot arm 20 along direction until the image coordinate of the sphere center 11 moves to _Os2 , as shown in FIG4A.

Rotate the rotary disk 50 degrees back to , and use the visual sensor 30 to determine the position of the center 11 of the sphere 10: if it has deviated from the coordinates , then return to step 4 to control the robot arm 20 to move the center 11 of the ball 10 between the A and B axes and finally converge to the intersection of the A and B axes, so that the center 11 is located at 50 degrees on the rotating disk. and When the coordinates of the visual sensor 30 meet and (At this time, the coordinates of the sphere center 11 relative to the reference coordinate system of the robot arm 20 are ), as shown in FIG4B, wherein I in FIG4B indicates that the visual sensor 30 is in the first position, II indicates that the visual sensor 30 is in the second position, and A is through and perpendicular to the vector of the visual sensor 30, B is a vector passing through And perpendicular to the vector of the visual sensor 30.

like , return to the above point 3, continue to collect different postures and the position of the ball center 11 The joint coordinate combination to obtain sufficient calibration information; if , the coordinates of the center 11 of the sphere 10 relative to the coordinate system of the flange surface 21 can be obtained using the kinematic equation.

…Equation 12.

in Substitute the j-th joint coordinate combination and the remaining DH parameters into the coordinate conversion matrix, which converts the coordinates from the flange surface 21 coordinate system to the robot arm 20 reference coordinate system; is the coordinate of the center 11 of the sphere 10 relative to the coordinate system of the flange surface 21, This means the rotating disk is 50 degrees. , The image coordinates of the sphere 10 and the center 11 in the visual sensor 30 are When , the coordinates of the center 11 of the sphere 10 relative to the reference coordinate system of the robot arm 20. Substituting the four sets of joint coordinates into Equation 12, we can obtain Equations 13 and 14.

…Formula 13.

…Equation 14.

in , for The pseudo-inverse matrix can be used to obtain the coordinates of the center 11 of the sphere 10 relative to the flange surface 21. , and the image coordinates of the center 11 of the sphere 10 on the two visual sensors 30 are respectively When the center 11 of the sphere 10 is relative to the reference coordinate system of the robot arm 20, .

Complete the center 11 of the sphere 10 Relative to the position calibration of the flange surface 21 coordinate system, obtain the coordinates After that, the contour sensor 40 and the visual sensor 30 can be used to simultaneously obtain the information of the sphere 10 to calibrate the positional relationship between the robot arm 20 and the contour sensor 40. The method of calibrating the reference coordinate system of the contour sensor 40 and the robot arm 20 is to first control the robot arm 20 to move the sphere 10 to a position where the contour sensor can capture the contour, and at the same time obtain the center 11 of the sphere 10. The coordinates relative to the reference coordinate system of the robot arm 20 and the coordinates relative to the coordinate system of the contour sensor 40 , by obtaining several different positions and The calibration is then completed, and Respectively represent the center 11 of the sphere 10 at the k-th position With respect to the coordinates of the reference coordinate system of the robot arm 20 and the coordinate system of the contour sensor 40, the process is as follows:

make , control the robot arm 20 to move the ball 10 to a position where the contour sensor and any one of the visual sensors 30 can simultaneously read the information of the ball 10.

Record the center 11 of the sphere 10 relative to the reference coordinate system of the robot arm 20 Coordinates .

The contour sensor 40 is used to capture the contour information of the ball 10 and obtain the coordinate system relative to the contour sensor 40. Contour point data set information , and the circle equation Use RANSAC (Random Sample Consensus) to perform minimum error fitting and obtain the center coordinates of the circle and cross-sectional radius , as shown in Figure 5A.

The distance between the sphere center 11 and a contour sensing plane P is calculated using the Pisces theorem as shown in Equation 15:

…Formula 15.

in is the radius of the sphere, is the height of the center 11 of the sphere 10 relative to the sensing plane. From Equation 15, we can see that the two solutions obtained represent whether the center 11 is located above or below the contour sensing plane P. Therefore, the information of the sphere 10 obtained by the visual sensor 30 can be used to assist in the judgment to obtain the correct solution. As shown in Figure 5B, the image of the sphere 10 obtained by the visual sensor 30 is used to determine the center position through image processing methods and compared with the laser line projected on the sphere 10 by the contour sensing plane P. If the center position is higher than the laser line, it means that , vice versa .

Record the coordinates of this coordinate relative to the contour sensor coordinate system as .

make

a. If , control the robot arm 20 to After that, follow Move any distance in the direction and return to step 2.

b. If , control the robot arm 20 to After clicking, follow the 20 coordinate system of the robot arm Plane, and Move any length in any direction and return to step 2.

c. If , control the robot arm 20 to After clicking, move any distance in any direction and return to step 2.

like ,calculate Relative to Unit vector and two vectors perpendicular to this vector .

…Formula 16.

…Formula 17.

…Formula 18.

will Change to Direction expression, and obtain The origin of the coordinate system and The relationship between the origin of the coordinate system is shown in Figure 5C.

…Formula 19.

The coordinates of the contour sensor 40 can be obtained Convert to the reference coordinate system of the robot arm 20 Coordinate transformation matrix.

…Formula 19.

In step S3, the contour sensor 40 is determined and the reference coordinate system of the robot arm 20 After the conversion relationship, the calibration of the tool T coordinate system can be started; the method proposed in the present invention will explain how to calibrate the tool T with a cylindrical shape and a flat axial end to obtain the tool axis when the tool T is installed on the robot arm 20, and the center point coordinates of the tool T (the intersection of the tool axis and the end plane).

The calibration method proposed by the present invention first moves the tool T into the scanning range of the contour sensor 40 and analyzes the obtained contour and its equation through RANSAC: If the obtained contour is a straight line after fitting, it means that the obtained contour is located on the A surface (bottom surface) or and At this time, the relationship between the current sensing plane of the contour sensor 40 and the tool T can be confirmed by the external visual sensor 30 (the 2D visual sensor 30 with the same viewing angle as Figure 2). The definition of the tool T is shown in Figure 6: (1) If the sensing plane is located on the A surface of the tool T (indicated by A in Figure 6), the robot can be controlled to orbit or Rotate until the resulting contour fit is an ellipse or a circle; (2) If and parallel, the robot arm 20 is controlled to make the tool T rotate around Rotate the axis until the contour fitting result is an ellipse or a circle, which means that the contour scanning range is located on the B surface (B in Figure 6).

When the obtained contour is located on the B surface, the tool T axis direction can be calibrated by controlling the movement of the robot arm 20 so that the tool T axis direction With the contour sensor 40 The calibration can be completed if the directions are consistent. The process is as follows:

The sensing point data obtained by the contour sensor 40 is fitted to a minimum error ellipse using RANSAC to obtain a fitting equation, as shown in FIG7A and Equation 21, where M in FIG7A represents the major axis of the ellipse and m represents the minor axis of the ellipse.

…Formula 21.

in is the coefficient of the ellipse equation. Then the coefficient of the ellipse equation can be used to find the length of the major axis of the ellipse. , length of the minor axis of the ellipse , the major axis of the ellipse and the profile sensor 40 Angle , and the coordinates of the center of the ellipse , as shown in Equations 22 to 26.

…Formula 22.

…Formula 23.

…Formula 24.

…Formula 25.

…Formula 26.

Among them, if and , which indicates the major axis of the ellipse and the coordinate axis of the contour sensor 40 coordinate system Angle .

The center coordinates of the ellipse relative to the profile scanner With the short axis direction Converted into directions relative to the reference coordinate system of the robot arm 20 and direction , as shown in Equations 27 and 28, where It can be obtained by formula 20.

…Formula 27.

…Formula 28.

Control the robot arm 20 so that the center point of the ellipse Fixed and along the minor axis of the ellipse Rotation, as shown in Figure 7B, on the contour sensing plane P, if the length of the long axis after rotation is greater than the length of the long axis in the initial state, or the contour sensing information changes from an ellipse to a straight line, then change the rotation , until the length of the major axis and minor axis of the ellipse are equal, which represents the T-axis direction of the tool With the contour sensor 40 The direction of the tool T axis relative to the coordinate system of the flange surface 21 of the robot arm 20 can be obtained. , as shown in Equations 29 and 30:

…Formula 29.

…Formula 30.

Since the tool T axis direction With the contour sensor 40 direction is parallel to the T axis of the tool. The direction after being expressed in the coordinate system of the contour sensor 40 is ,in and They are and by Indicates the direction, for by Indicates the direction.

When the tool axis direction is obtained After that, just define and The direction of the tool T coordinate system can be obtained. Since the tool T is cylindrical, and Just define Just vertically:.

*like Not with If the tool T coordinate system is close to parallel, and Then we can define it as Equations 31 and 32:

…Formula 31.

…Formula 32.

*like and If the tool T coordinate system is close to parallel, and It can be defined as Equations 33 and 34, where :

…Formula 33.

…Formula 34.

After the tool T axis direction calibration is completed, the tool T center point position calibration can be started: first control the robot arm 20 to or and parallel, Ze Yu Any angle (in ), and then the robot arm 20 is controlled by the information of the vision sensor 30 to move the tool T into the sensing range of the contour sensor 40 so that the contour sensed contour is located on the B surface to obtain the contour information of the tool T.

The visual sensor 30 is used to determine the relationship between the contour sensing plane P and the tool T. If the contour sensing plane P passes through the A surface or the C surface of the tool T (marked C in FIG6 ), it means that the intersection curve of the contour sensing plane P and the contour of the tool T is not a complete elliptical curve, as shown on the left side of FIG7C .

If the contour sensing plane P passes through the A surface or C surface of the tool T, the robot arm 20 is controlled to move along or Direction translation, so that the intersection curve of the contour sensing plane P and the contour of the tool T intersects at the B surface of the tool T, as shown in Figure 7D; or Direction translation, the intersection curve of the sensing plane and the tool T will contain the A or C surface contour of the tool T, then change Angle, so that the intersection curve of the contour sensing plane P and the contour of the tool T intersects at the B surface of the tool T.

After the tool T is moved to a position and angle where a complete elliptical contour can be obtained, the robot arm 20 is then controlled to move the tool T along Direction translation Then, the robot arm 20 is controlled to fix the intersection of the tool T axis and the sensing plane, and the tool T is moved along the contour sensor 40. Repeat this process until a straight line segment appears in the contour state, as shown in the right side of Figure 7C and Figure 7E.

The rotating disk 50 is rotated 360 degrees so that the contour sensor 40 can obtain the complete intersection curve between the sensing plane and the contour of the tool T. Then, the contour of the B surface of the tool T outside the straight line segment (the A surface of the tool T) is subjected to RANSAC to obtain the ellipse contour equation and determine the relationship between the straight line and the ellipse.

If the elliptical contour obtained by contour sensing is smaller than a semi-ellipse (as shown on the left side of Figure 7F), then Direction translation to increase the elliptical contour sensing range and return to step 9; if the elliptical contour sensed is larger than a semi-ellipse (as shown on the right side of Figure 7F), then Shift in the direction to reduce the ellipse contour sensing range and return to step 9. If the ellipse contour sensed is equal to a semi-ellipse, proceed to step 11.

When the elliptical contour obtained by contour sensing is equal to a semi-ellipse, the coordinates of the ellipse center are This is the intersection of the tool T axis and the A surface of the tool T. Therefore, the coordinate of the tool T center point relative to the flange surface 21 of the robot is As shown in Formula 35, the calibration of the tool T axis and the tool T center can be completed.

…Formula 35.

Furthermore, unless expressly stated otherwise, the order of the components, elements, sequences, the use of numerals, or other names described herein are not intended to limit the order of the processes and methods of the present invention. Although the above text discusses some currently considered useful embodiments of the invention through various examples, it should be understood that such details are for illustrative purposes only, and the present invention is not limited to the disclosed embodiments but also encompasses equivalent related variations and modifications.

In some embodiments, numbers are used to describe the quantity of components and attributes. It should be understood that such numbers used in the description of the embodiments are modified in some examples using the modifiers "approximately", "approximately" or "substantially". Unless otherwise stated, "approximately", "approximately" or "substantially" indicate that the numbers are allowed to vary by ±20%. Accordingly, in some embodiments, the numerical parameters used in the description and the claims are approximate values, which may change according to the required characteristics of the individual embodiments. In some embodiments, the numerical parameters should consider the specified significant digits and adopt the general digit retention method. Although the numerical domains and parameters used to confirm the breadth of the scope of some embodiments of the present invention are approximate values, in specific embodiments, the settings of such numerical values are as accurate as possible within the feasible range.

Finally, it should be understood that the embodiments described herein are intended only to illustrate the principles of the present invention. Other variations are also possible within the scope of the present invention. Therefore, by way of example and not limitation, alternative configurations of the present invention may be considered consistent with the teachings of the present invention. Accordingly, the embodiments of the present invention are not limited to those expressly shown and described herein.

10 Sphere 11 Center of Sphere 20 Robot Arm 21 Flange 30 Vision Sensor 40 Profile Sensor 50 Rotary Plate I and II Vision Sensor Positions M and m Ellipse Major and Minor Axes P Profile Sensing Plane T Tool Steps S1-S3

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some examples or embodiments of the present invention, and are not absolutely used to limit the technical scope of the present invention. Unless it is obvious from the preceding and following texts or otherwise explained, the same reference numerals in the figures represent the same structure or operation. Among them: Figure 1 is a step flow chart of the calibration method for a tool without a tool tip point of the present invention. Figure 2 is a schematic diagram of the device used in the calibration method for a tool without a tool tip point of the present invention. Figure 3A is a system architecture diagram of the calibration method for a tool without a tool tip point of the present invention. Figure 3B is a diagram of the calibration method for a tool without a tool tip point of the present invention. Yu 3C is a schematic diagram showing the relationship between the rotation angle θ _ri and the rotating disk in the calibration method for the tool without a tool tip point of the present invention. FIG4A is a schematic diagram showing the movement direction of the vision sensor in the calibration method for the tool without a tool tip point of the present invention. FIG4B is a schematic diagram showing the control of the center movement of the sphere and convergence to the vision sensor coordinates O _s1 , O _s2 in the calibration method for the tool without a tool tip point of the present invention. FIG5A is a schematic diagram showing the fitting of the sphere information captured by the contour sensor and the sphere contour information in the calibration method for the tool without a tool tip point of the present invention. FIG5B is a schematic diagram showing the relationship between the sphere captured by the vision sensor and the laser scanning line of the contour sensor in the calibration method for the tool without a tool tip point of the present invention. FIG5C is a schematic diagram showing the relationship between the sphere captured by the vision sensor and the laser scanning line of the contour sensor in the calibration method for the tool without a tool tip point of the present invention. The origin of the coordinate system and Schematic diagram of the relationship between the origin of the coordinate system. Figure 6 is the tool definition of the tool coordinate system calibration system in the calibration method of the tool without a tool tip point of the present invention. Figure 7A is the contour (circle point) and the fitting result (solid point) obtained by the contour sensor in the calibration method of the tool without a tool tip point of the present invention. Figure 7B is the center point of the ellipse sensed by controlling the robot arm in the calibration method of the tool without a tool tip point of the present invention. FIG7C is a schematic diagram illustrating the system state of an incomplete elliptical contour in the calibration method for a tool without a tool tip point according to the present invention. FIG7D is a schematic diagram illustrating the contour state of an incomplete elliptical contour in the calibration method for a tool without a tool tip point according to the present invention. FIG7E is a schematic diagram illustrating the system state of obtaining a complete elliptical contour in the calibration method for a tool without a tool tip point according to the present invention. FIG7F is a schematic diagram illustrating the system state of controlling the robot arm to translate along the + _zp direction until a straight line contour appears in the calibration method for a tool without a tool tip point according to the present invention.

S1-S3: Steps

Claims (9)

A method for calibrating the center of a tool without a tool tip on a robotic arm comprises the following steps: Step 1: Mounting a sphere of known radius on a flange surface of a robotic arm and using a vision sensor to obtain information about the sphere and calibrate the coordinates of the sphere's center relative to the flange surface of the robotic arm; Step 2: Simultaneously obtaining information about the sphere using a profile sensor and the vision sensor, and combining the information from the profile sensor and the vision sensor to calibrate the relative positional relationship between the robotic arm and the profile sensor; and Step 3: Finally, a tool required for the actual application is mounted on the flange surface of the robot arm. The vision sensor and the profile sensor are used to obtain tool information. Based on this information, corresponding control instructions are generated to move the tool to a specified position. This calibrates the tool axis and the tool center point, completing the calibration of the tool without a tool tip point. A method for calibrating the center of a tool without a tool tip point of a robotic arm as described in claim 1, wherein: in step 1, image information from the visual sensor at two different viewing angles is used to control the movement of the robotic arm, ultimately causing the center of the sphere to reach the same position in space in four different postures, thereby obtaining the coordinates of the center of the sphere relative to the flange surface. A method for calibrating the tool center of a robot arm without a tool tip as described in claim 1 or 2, wherein: the position of the center of the sphere is calibrated by using a rotating disk to change the viewing angle of the visual sensor, controlling the movement of the robot arm with two different viewing angles so that the center of the sphere reaches the same position in space with different postures, and finally obtaining the coordinates of the center of the sphere through kinematic equations. A method for calibrating the center of a tool without a tool tip point of a robotic arm as described in claim 2, wherein: the robotic arm is moved so that the center of the sphere is within the field of view and as far away from the image boundary as possible. A method for calibrating a tool center without a tool tip point of a robot arm as described in claim 1, wherein: in step 2, motion control is performed based on information obtained by a contour sensor, and a relative relationship between a contour sensor coordinate system and a robot arm reference coordinate system is obtained to convert the command into a command relative to the robot arm reference coordinate system. A method for calibrating the tool center of a robot arm without a tool tip point as described in claim 1, wherein: before calibrating the relative position of the contour sensor and the robot arm, the coordinates of the center of the sphere mounted on the flange surface of the robot arm relative to a flange surface coordinate system are obtained. A method for calibrating the tool center of a robot arm without a tool tip point as described in claim 1 or 2, wherein: the position of the center of the sphere relative to a flange surface coordinate system is calibrated, and after obtaining the coordinates, the sphere information is simultaneously obtained using the contour sensor and the visual sensor to calibrate the positional relationship between the robot arm and the contour sensor. A method for calibrating the tool center of a robot arm without a tool tip point as described in claim 1 or 2, wherein: calibrating the contour sensor and a robot arm reference coordinate system includes controlling the robot arm to move the sphere to a position where the contour sensor can capture the contour, and simultaneously obtaining the coordinates of the center of the sphere relative to the robot arm reference coordinate system and the coordinates relative to a contour sensor coordinate system, and completing the calibration by obtaining several different positions. A method for calibrating the tool center of a robot arm without a tool tip point as described in claim 1 or 2, wherein: after determining the conversion relationship between the contour sensor and a robot arm reference coordinate system, a tool coordinate system is calibrated.