CN111157004B - Tool calibration method for flange downward four-axis robot - Google Patents
Tool calibration method for flange downward four-axis robot Download PDFInfo
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- CN111157004B CN111157004B CN201911413459.3A CN201911413459A CN111157004B CN 111157004 B CN111157004 B CN 111157004B CN 201911413459 A CN201911413459 A CN 201911413459A CN 111157004 B CN111157004 B CN 111157004B
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- 238000000034 method Methods 0.000 title claims abstract description 19
- 239000011159 matrix material Substances 0.000 description 8
- 238000000691 measurement method Methods 0.000 description 2
- 230000036544 posture Effects 0.000 description 2
- 230000009466 transformation Effects 0.000 description 2
- 238000009795 derivation Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000002427 irreversible effect Effects 0.000 description 1
Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
- G01C21/00—Navigation; Navigational instruments not provided for in groups G01C1/00 - G01C19/00
- G01C21/20—Instruments for performing navigational calculations
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B21/00—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant
Abstract
A tool calibration method of a flange downward four-axis robot comprises the following steps: a. operating the robot, enabling the tail end point of the robot tool to be calibrated to respectively move to the same spatial position point when the robot is in at least two different pose states, and recording pose data of a flange coordinate system of the robot in each pose state; b. and c, obtaining the distance X from the Z axis of the tool coordinate system to the X axis of the flange coordinate system and the distance Y from the Z axis of the tool coordinate system to the Y axis of the flange coordinate system according to the pose data obtained in the step a. The invention can calibrate the tool of the four-axis robot with the flange facing downwards, and has simple calibration process and high calibration efficiency.
Description
Technical Field
The invention relates to a tool calibration technology of a robot.
Background
For the coordinate system of the tool installed at the tail end of the robot, the origin and the direction of the tool are continuously changed along with the position and the angle of the tail end, the coordinate system is actually obtained by changing the basic coordinate system through rotation and translation, namely, the coordinate system of the tool can be determined by determining the rotation mode, the angle, the translation direction and the distance. The process of determining the rotation mode, angle and translational direction and distance of the tool coordinate system relative to the base coordinate system is called tool calibration.
Currently, each robot manufacturer has different methods for tool calibration, such as a three-point method, a six-point method, an eight-point method and the like, and the main principle is to solve a tool coordinate system by obtaining end pose of a plurality of robots and simultaneous equations. For a six-axis robot, the difference of the positions and the postures of a plurality of ends of the robot is required to be as large as possible, so that the fact that a plurality of points have no correlation is guaranteed, matrix reversibility is guaranteed in matrix operation in simultaneous equations, and a tool coordinate system is available. For a four-axis robot with a downward end flange (as shown in fig. 1), since the end flange cannot move around the x-axis and the y-axis of the world coordinate system, if the tool calibration method is adopted, all the pose have correlation, so that the matrix is irreversible during operation, and the tool coordinate system cannot be solved. Therefore, in current practice, the tool coordinate system is usually calculated by manually measuring the tool size without tool calibration for the four-axis robot.
Disclosure of Invention
The invention aims to provide a method for calibrating a tool of a four-axis robot with a downward flange.
In order to solve the technical problems, the invention adopts the following technical scheme:
the invention provides a tool coordinate system calibration method of a flange downward four-axis robot, which comprises the following steps:
a. operating the robot, enabling the tail end point of the robot tool to be calibrated to respectively move to the same spatial position point when the robot is in at least two different pose states, and recording pose data of a flange coordinate system of the robot in each pose state;
b. and c, obtaining the distance X from the Z axis of the tool coordinate system to the X axis of the flange coordinate system and the distance Y from the Z axis of the tool coordinate system to the Y axis of the flange coordinate system according to the pose data obtained in the step a.
The invention has at least the following advantages:
the invention has simple calibration process, high calibration efficiency and good calibration precision.
Drawings
Fig. 1 shows an external schematic view of a four-axis robot with a flange facing down.
Fig. 2 shows a schematic diagram of the relationship of the base coordinate system, the flange coordinate system and the tool coordinate system.
Detailed Description
The invention will now be described in detail with reference to the drawings and specific examples.
Fig. 1 shows an external schematic view of a four-axis robot with a flange facing down. It can be seen from the figure that due to the structural design the flange 9 of the four-axis robot will always be oriented downwards, i.e. only rotate around the Z-axis of the flange coordinate system and not around the X-axis and the Y-axis.
Since the flange of the four-axis robot cannot rotate around the X-axis and the Y-axis in the base coordinate system, the XOY-plane of the tool coordinate system is parallel to the XOY-plane of the base coordinate system, and the TCP point (i.e., the tool end point, tool Center Point) of the calibration tool becomes the Z-axis position of the calibration tool coordinate system, the distance of the TCP point on the Z-axis from the origin of the flange coordinate system, and the angle of the X-axis of the tool coordinate system and the X-axis of the flange coordinate system. The calibration of the tool coordinate system only requires the determination of the following parameters:
x—distance of the Z axis of the tool coordinate system to the X axis of the flange coordinate system.
y—distance of Z-axis of tool coordinate system to Y-axis of flange coordinate system.
z—the Z-direction distance of the tool's TCP point from the origin of the flange coordinate system.
w-the angle between the X-axis of the tool coordinate system and the X-axis of the flange coordinate system.
In this embodiment, the calibration process for the distance X from the Z axis of the tool coordinate system to the X axis of the flange coordinate system and the distance Y from the Z axis of the tool coordinate system to the Y axis of the flange coordinate system is as follows:
a. operating the robot, enabling the tail end point of the robot tool to be calibrated to move to the same spatial position point respectively when the robot is in two different pose states, and recording pose data of a flange coordinate system of the robot in each pose state;
b. and c, calculating the distance X from the Z axis of the tool coordinate system to the X axis of the flange coordinate system and the distance Y from the Z axis of the tool coordinate system to the Y axis of the flange coordinate system according to the pose data obtained in the step a, wherein the specific formula is as follows:
wherein X0 is the projection distance of the origin of the flange coordinate system in the first pose state on the X axis of the base coordinate system, Y0 is the projection distance of the origin of the flange coordinate system in the first pose state on the Y axis of the base coordinate system, and w0 is the angle of the flange coordinate system in the first pose state around the Z axis of the base coordinate system; x1 is the projection distance of the origin of the flange coordinate system in the second pose on the X axis of the base coordinate system, Y1 is the projection distance of the origin of the flange coordinate system in the second pose on the Y axis of the base coordinate system, and w1 is the angle of the flange coordinate system in the second pose around the Z axis of the base coordinate system.
The principle and derivation of the above formula is as follows.
Referring to fig. 2, B represents a base coordinate system, F0 represents coordinates of a pose 0 of the flange in the base coordinate system as (X0, Y0, w 0), wherein X0 is a projection distance of an origin of the flange coordinate system in the pose 0 state on an X axis of the base coordinate system, Y0 is a projection distance of the origin of the flange coordinate system in the pose 0 state on a Y axis of the base coordinate system, and w0 is an angle of the flange coordinate system in the pose 0 state around a Z axis of the base coordinate system; f1 represents that the coordinates of the pose 1 of the flange in the base coordinate system are (X1, Y1, w 1), wherein X1 is the projection distance of the origin of the flange coordinate system in the pose 1 state on the X axis of the base coordinate system, Y1 is the projection distance of the origin of the flange coordinate system in the pose 1 state on the Y axis of the base coordinate system, and w1 is the angle of the flange coordinate system in the pose 1 state around the Z axis of the base coordinate system. The fixed axis is the Z axis of the tool coordinate system, and the coordinates of the Z axis in the flange coordinate system are (x, y) and are fixed.
The relation among the tool coordinate system, the flange coordinate system and the base coordinate is as follows
B T T ＝ B T F · F P T (1)
Wherein T is a homogeneous transformation matrix, B T T representing the transformation matrix of the base coordinate system B to the tool coordinate system T. F P T Is the coordinate of the origin of the tool coordinate system in the flange coordinate system.
Then the flange pose 0 and the flange pose 1 brought into the formula (1) are
Expanding the matrix to obtain
Wherein, B R F0 is a rotation matrix of the position and the posture 0 of the flange in the basic coordinate system, B L F0 translation vector of the flange in pose 0 under the basic coordinate system is based on the relation shown in fig. 2, and the fact that the actual flange always faces to the negative Z-axis direction under the basic coordinate system is considered
Z is the Z-axis projection distance of the current robot flange based on the base coordinate system. Parameters under the pose 1 can be obtained by the same way, and are put into a formula (3) to be arranged to obtain
The first two are combined to obtain x and y as
In other embodiments, a matrix operation or other method may be used to solve for the distance X from the Z axis of the tool coordinate system to the X axis of the flange coordinate system and the distance Y from the Z axis of the tool coordinate system to the Y axis of the flange coordinate system. In addition, more than two pose points can be adopted, and the aim of further improving the calibration precision can be achieved by solving in an average value mode.
The projection distance of the TCP on the Z axis in the tool coordinate system may be obtained by an external measurement method, or the angle between the X axis of the tool coordinate system and the X axis of the base coordinate system may be obtained by an external measurement method (for example, the robot observes the range of values in the base coordinate system).
The workflow of the invention is described below in connection with a specific example of application.
Mounting the tool on a flange of the four-axis robot, and selecting a terminal point of the robot tool to be calibrated on the tool;
the robot is clicked, the tail end point of the robot tool to be calibrated touches the needle point, and the X-axis coordinate value and the Y-axis coordinate value of the flange coordinate system under the base coordinate system at the moment and the angle of the flange coordinate system around the Z-axis of the base coordinate system under the base coordinate system are recorded; wherein, the X-axis coordinate value and the Y-axis coordinate value of the flange coordinate system under the base coordinate system are respectively equal to X0 and Y0 described in the formula (6), and the angle of the flange coordinate system around the Z axis of the base coordinate system under the base coordinate system is equal to w0 described in the formula (6);
rotating the four axes of the robot to enable the tail end point of the robot tool to be calibrated to touch the needle point in another pose, and recording X-axis coordinate values and Y-axis coordinate values of the flange coordinate system under the base coordinate system at the moment and angles of the flange coordinate system around the Z axis of the base coordinate system under the base coordinate system; wherein, the X-axis coordinate value and the Y-axis coordinate value of the flange coordinate system under the base coordinate system are respectively equal to X1 and Y1 described in the formula (6), and the angle of the flange coordinate system around the Z axis of the base coordinate system under the base coordinate system is equal to w1 described in the formula (6);
according to the formula (6), the distance X from the Z axis of the tool coordinate system to the X axis of the flange coordinate system and the distance Y from the Z axis of the flange coordinate system are obtained;
the robot is clicked, so that the flange and the needle point are positioned on the same horizontal plane, and the change quantity of the Z-axis coordinate value under the basic coordinate system is recorded and used as the distance Z from the origin of the flange coordinate system to the origin of the tool coordinate system;
rotating the tool to an initial angle position of a tool coordinate system, and recording a current angle as an included angle between an X axis of the tool coordinate system and an X axis of a flange coordinate system;
and inputting the result to a demonstrator.
Claims (4)
1. The tool calibration method of the flange downward four-axis robot is characterized by comprising the following steps of:
a. operating the robot, enabling the tail end point of the robot tool to be calibrated to respectively move to the same spatial position point when the robot is in at least two different pose states, and recording pose data of a flange coordinate system of the robot in each pose state;
b. c, according to the pose data obtained in the step a, obtaining the distance X from the Z axis of the tool coordinate system to the X axis of the flange coordinate system and the distance Y from the Z axis of the tool coordinate system to the Y axis of the flange coordinate system;
wherein, the distance X from the Z axis of the tool coordinate system to the X axis of the flange coordinate system and the distance Y from the Y axis of the flange coordinate system are calculated by the following formulas:
wherein X0 is the projection distance of the origin of the flange coordinate system in the first pose state on the X axis of the base coordinate system, Y0 is the projection distance of the origin of the flange coordinate system in the first pose state on the Y axis of the base coordinate system, and w0 is the angle of the flange coordinate system in the first pose state around the Z axis of the base coordinate system; x1 is the projection distance of the origin of the flange coordinate system in the second pose state on the X axis of the base coordinate system, Y1 is the projection distance of the origin of the flange coordinate system in the second pose state on the Y axis of the base coordinate system, and w1 is the angle of the flange coordinate system in the second pose state around the Z axis of the base coordinate system;
c. acquiring a z-direction distance from an origin of a flange coordinate system to an origin of a tool coordinate system;
d. and acquiring an included angle between the X axis of the tool coordinate system and the X axis of the flange coordinate system.
2. The method for calibrating a tool of a flange-down four-axis robot according to claim 1, wherein the step a comprises the steps of:
a-1, mounting a tool on a flange of a four-axis robot;
a-2, a robot is clicked, the tail end point of the robot tool to be calibrated is enabled to touch the needle point, and the X-axis coordinate value and the Y-axis coordinate value of the flange coordinate system under the base coordinate system and the angle around the Z-axis of the base coordinate system under the base coordinate system are recorded;
and a-3, rotating the four axes of the robot, enabling the tail end point of the robot tool to be calibrated to touch the needle point in another pose, and recording X-axis coordinate values and Y-axis coordinate values of the flange coordinate system under the base coordinate system and angles around the Z axis of the base coordinate system under the base coordinate system.
3. The method for calibrating a tool of a flange-down four-axis robot according to claim 2, comprising:
c. the robot is turned on, so that the flange and the needle point are positioned on the same horizontal plane, and the change of the Z-axis coordinate value under the base coordinate system is recorded and used as the Z-direction distance from the origin of the flange coordinate system to the origin of the tool coordinate system.
4. The method for calibrating a tool of a flange-down four-axis robot according to claim 1, comprising:
d. and rotating the tool to an initial angle position of the tool coordinate system, and recording the current angle as an included angle between the X axis of the tool coordinate system and the X axis of the flange coordinate system.
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