CN113091670B - Calibration device and calibration method for robot joint stiffness - Google Patents
Calibration device and calibration method for robot joint stiffness Download PDFInfo
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- CN113091670B CN113091670B CN202110395144.1A CN202110395144A CN113091670B CN 113091670 B CN113091670 B CN 113091670B CN 202110395144 A CN202110395144 A CN 202110395144A CN 113091670 B CN113091670 B CN 113091670B
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Abstract
The invention relates to a calibration device and a calibration method for robot joint stiffness. The method comprises the following steps: the method comprises the following steps of initially calibrating a closed-loop measuring device by utilizing a calibration block, and recording joint angles corresponding to a plurality of calibration points and calibration displacement variable quantity measured by a displacement sensor in the closed-loop measuring device; replacing different mass blocks at the tail end of the serial robot, applying different loads to the tail end of the robot, driving the tail end of the robot to reach a calibration point by utilizing a joint angle, and acquiring the current displacement variation; determining the offset generated at the tail end of the robot according to the calibration displacement variation and the current displacement variation based on the measurement coordinate system and the calibration block coordinate system; based on a plurality of different coordinate systems, the actual joint stiffness of the series robot is calibrated according to the joint angle, the offset generated by the tail end of the robot and the force or moment born by the tail end of the robot under different loads. The invention can simplify the calibration process and reduce the calibration cost.
Description
Technical Field
The invention relates to the field of robots, in particular to a calibration device and a calibration method for robot joint stiffness.
Background
Under the background of rapid development in the high-end manufacturing field, an industrial robot can be embedded into an automatic production line as a flexible unit, and the cost of the industrial robot is usually lower than the price of a set of professional clamp and a numerical control machine tool. In addition, most machine tools have limited movement space and low flexibility, usually have 3 to 5 degrees of freedom, cannot process some complex curved workpieces, and the robot has a large working space, generally has 6 degrees of freedom, and can drive a tool to reach any attitude in space. However, the industrial robot is influenced by the inherent characteristics of the serial structure, the rigidity of the industrial robot is usually only 1/50-1/20 of a numerical control machine tool, and the structural characteristics of weak rigidity cause the industrial robot to have low bearing capacity to working load. For an industrial robot facing the high-precision machining field, machining defects such as obviously low machining precision, poor surface machining quality and the like of the robot can be caused by the rigidity characteristic of the robot body. The rigidity characteristic of the robot is researched, and particularly, the recognition and improvement of the rigidity of the robot are of great significance to the manufacturing and processing industry. The rigidity characteristic of the robot is researched, joint rigidity parameters of the robot are often calibrated firstly, and then the error compensation is carried out on a deformed joint angle generated when the tail end of the robot bears load, so that the absolute positioning accuracy of the robot is improved. Currently, there are studies on calibration of stiffness parameters of robots in literature, and most of these methods perform stiffness calibration by obtaining a pose variation of a robot end through measurement of a laser tracker, however, the prior art has the following problems:
(1) in the traditional joint stiffness calibration method, an expensive external metering system such as a laser tracker is generally used for measuring the terminal pose of the robot, the calibration process is complex to operate, professional personnel are required to operate, and the calibration cost is increased. The laser tracker also has requirements on the use environment, and the application occasions are limited.
(2) For the measurement of the load borne by the tail end of the robot, equipment such as a six-dimensional force sensor or a dynamometer is generally used, and the cost of joint rigidity calibration is increased.
Disclosure of Invention
The invention aims to provide a calibration device and a calibration method for robot joint stiffness, and aims to solve the problems of complex joint stiffness calibration process and high calibration cost.
In order to achieve the purpose, the invention provides the following scheme:
a calibration device for rigidity of a robot joint comprises: the system comprises a serial robot, an inclined plane base, an experiment platform, a closed loop measuring device and a clamping plate bracket;
the inclined plane base and the clamping plate bracket are arranged on the experiment platform; the series robot is arranged on the inclined plane base, a mass block is arranged between the tail end of the series robot and the closed-loop measuring device, and the mass block is used for applying load to the tail end of the series robot; the closed-loop measuring device is supported by the splint support, a calibration block is arranged in the closed-loop measuring device and used for calibrating the tail end of the series robot, and the closed-loop measuring device is used for calibrating the joint rigidity of the series robot.
Optionally, the closed-loop measurement apparatus specifically includes: the clamp plate group, the displacement sensor, the inner hexagon screw, the positioning pin and the movable plate;
the clamping plate group comprises three clamping plates, and every two adjacent virtual cubes are formed by the three clamping plates; the movable plate is arranged on any side surface of the virtual cube;
each clamping plate is provided with the displacement sensor; each displacement sensor is in contact with the plane of the calibration block and is used for measuring the displacement variation of the movement of the calibration block;
the inner hexagonal screw and the positioning pin are arranged on the movable plate, and the movable plate is used for driving the calibration block to move.
Optionally, the method further includes: initially calibrating a connecting piece;
the initial calibration connecting piece is arranged on the movable plate and fixedly connected with the initial calibration connecting piece and the calibration block through the inner hexagonal screw and the positioning pin.
Optionally, the method further includes: a terminal connector;
the end connecting piece is used for connecting the serial robot and the calibration block; the mass block is arranged between the tail end of the serial robot and the tail end connecting piece.
A calibration method for robot joint stiffness is applied to a calibration device for robot joint stiffness, and comprises the following steps: the system comprises a serial robot, an inclined plane base, an experiment platform, a closed loop measuring device and a clamping plate bracket; the inclined plane base and the clamping plate bracket are arranged on the experiment platform; the series robot is arranged on the inclined plane base, a mass block is arranged between the tail end of the series robot and the closed-loop measuring device, and the mass block is used for applying load to the tail end of the series robot; the closed-loop measuring device is supported by the splint support, a calibration block is arranged in the closed-loop measuring device and used for calibrating the tail end of the serial robot, and the closed-loop measuring device is used for calibrating the joint rigidity of the serial robot;
the calibration method of the robot joint stiffness comprises the following steps:
establishing a robot base coordinate system, a robot tail end coordinate system, a measurement coordinate system of a closed-loop measuring device, a calibration block coordinate system and a robot tail end load application point coordinate system;
the calibration block is utilized to perform initial calibration on the closed-loop measuring device, and joint angles corresponding to a plurality of calibration points of the serial robot and calibration displacement variation measured by a displacement sensor in the closed-loop measuring device are recorded;
replacing different mass blocks at the tail end of the series robot, applying different loads to the tail end of the series robot, driving the tail end of the series robot to reach a calibration point by utilizing the joint angle, and acquiring the current displacement variation measured by a displacement sensor in the closed-loop measuring device;
determining the offset generated at the tail end of the serial robot according to the calibration displacement variable quantity and the current displacement variable quantity based on the measurement coordinate system and the calibration block coordinate system;
and calibrating the actual joint stiffness of the series robot according to the joint angle, the offset generated by the tail end of the series robot and the force or moment borne by the tail end of the series robot under different loads based on the robot base coordinate system, the robot tail end coordinate system, the calibration block coordinate system and the robot tail end applied load point coordinate system.
Optionally, the initially calibrating the closed-loop measuring device by using the calibration block, and recording joint angles corresponding to the multiple calibration points of the serial robot and a calibration displacement variation measured by a displacement sensor in the closed-loop measuring device, and then further including:
and determining the relative pose of the calibration block coordinate system of each calibration point relative to the measurement coordinate system by using a least square method according to the calibration displacement variation.
Optionally, the determining, according to the calibration displacement variation, the relative pose of the calibration block coordinate system of each calibration point with respect to the measurement coordinate system by using a least square method specifically includes:
determining a plane equation of a calibration block plane according to the serial robot under the calibration block coordinate system, and randomly selecting a position point vector on the calibration block plane, wherein a normal vector of the calibration block plane is known;
converting the position point vector and the normal vector into a measurement coordinate system, and determining a plane equation of the plane equation in the measurement coordinate system according to the position point vector and the normal vector in the measurement coordinate system;
bringing the pen point position coordinates of the displacement sensor into a plane equation under the measurement coordinate system, and determining a relative pose relation between the calibration displacement variation and the calibration block relative to the measurement coordinate system;
establishing a pose model according to the relative pose relation;
and determining the calibration relative pose of the calibration block coordinate system of each calibration point relative to the measurement coordinate system by using a least square method according to the calibration displacement variation based on the pose model.
Optionally, the determining, based on the measurement coordinate system and the calibration block coordinate system, an offset generated at the end of the tandem robot according to the calibration displacement variation and the current displacement variation specifically includes:
determining the current relative pose of the calibration block coordinate system of each calibration point relative to the measurement coordinate system by using the pose model and a least square method according to the current displacement variation;
and determining the offset generated by the tail end of the tandem robot according to the current relative pose and the calibrated relative pose.
Optionally, the calibrating the actual joint stiffness of the tandem robot according to the joint angle, the offset generated at the end of the tandem robot, and the force or moment borne by the end of the tandem robot under different loads based on the robot base coordinate system, the robot end coordinate system, the calibration block coordinate system, and the robot end load application point coordinate system specifically includes:
converting the offset generated at the tail end of the series robot and the force or moment borne by the tail end of the series robot under different loads into a robot base coordinate system;
and calibrating the actual joint stiffness of the series robot by using the joint angle, the offset generated by the tail end of the series robot under the robot base coordinate system and the force or moment born by the tail end of the series robot under different loads.
Optionally, the calibrating the actual joint stiffness of the tandem robot according to the joint angle, the offset generated at the end of the tandem robot, and the force or moment borne by the end of the tandem robot under different loads based on the robot base coordinate system, the robot end coordinate system, the calibration block coordinate system, and the robot end load application point coordinate system further includes:
and compensating joint angular deformation of the series robot by using the actual joint stiffness.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects: the invention provides a calibration device and a calibration method for robot joint rigidity, which are used for calibrating the robot joint rigidity only by using a low-cost closed-loop measuring device without using expensive laser trackers and six-dimensional force sensors, thereby simplifying the calibration process, reducing the equipment cost and further reducing the calibration cost.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.
FIG. 1 is a structural diagram of a calibration device for stiffness of a robot joint provided by the invention;
FIG. 2 is a perspective view of a closed loop measurement device provided by the present invention;
FIG. 3 is an exploded perspective view of a closed loop measurement device provided by the present invention;
FIG. 4 is a perspective view of an initial calibration apparatus provided in the present invention;
FIG. 5 is an exploded perspective view of the initial calibration apparatus provided in the present invention;
FIG. 6 is a flowchart of a method for calibrating stiffness of a robot joint according to the present invention;
FIG. 7 is a flowchart of another method for calibrating stiffness of a robot joint according to the present invention;
FIG. 8 is a flowchart of a calibration block pose measurement algorithm based on a six-point positioning principle according to the present invention;
fig. 9 is a schematic diagram of a robot end calibration block pose measurement principle provided by the invention.
Description of the symbols: 1-a serial robot, 2-an inclined plane base, 3-an experimental platform, 4-a closed loop measuring device, 5-a splint bracket, 6-a calibration block, 7-a terminal connecting piece, 8-a mass block, 9-a displacement sensor, 10-a splint, 11-a hexagon socket screw, 12-a positioning pin and 13-an initial calibration connecting piece; { OBXBYBZBIs the base coordinate system of the robot, { O }EXEYEZEThe end coordinate system of the robot, { O }FXFYFZFIs the coordinate system of the point of application load at the end of the robot, { OMXMYMZMIs a coordinate system of a calibration block, { OCXCYCZCAnd the measurement coordinate system of the closed-loop measurement device.
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.
The invention aims to provide a calibration device and a calibration method for robot joint rigidity, which can simplify the calibration process and reduce the calibration cost.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
Fig. 1 is a structural diagram of a calibration device for robot joint stiffness, and as shown in fig. 1, the calibration device for robot joint stiffness comprises: the system comprises a serial robot, an inclined plane base, an experiment platform, a closed loop measuring device and a clamping plate bracket; the inclined plane base and the clamping plate bracket are arranged on the experiment platform; the series robot is arranged on the inclined plane base, a mass block is arranged between the tail end of the series robot and the closed-loop measuring device, and the mass block is used for applying load to the tail end of the series robot; the closed-loop measuring device is supported by the splint support, a calibration block is arranged in the closed-loop measuring device and used for calibrating the tail end of the series robot, and the closed-loop measuring device is used for calibrating the joint rigidity of the series robot. The series robot can be a multi-degree-of-freedom robot such as a six-degree-of-freedom robot or a seven-degree-of-freedom robot; the displacement sensor may be a contact digital sensor or a laser displacement sensor.
The structure of the closed-loop measuring device 4 is shown in fig. 2-3, and comprises a clamping plate bracket 5, a displacement sensor 9, a clamping plate 10, an inner hexagon screw 11 and a positioning pin 12. The basic process is as follows: the closed-loop measuring device 4 is composed of three clamping plates 10, and each clamping plate 10 is provided with a corresponding hole for fixing the displacement sensor 9. Each clamping plate 10 is designed with a stepped surface for matching installation, so that the three clamping plates 10 are ensured to be perpendicular to each other, and the three clamping plates 10 are positioned by positioning pins 12 and fixed by hexagon socket head cap screws 11. The inside forms a measuring nest. Measurement coordinate system { O) of the closed-loop measuring device 4CXCYCZCIs placed at the bottom corner of the measuring nest (i.e. at the intersection of the three clamping plates 10) see fig. 2. The measurement accuracy of the displacement sensor 9 can be up to 0.01mm or more.
The series robot 1 can be connected with a computer through a TCP port, and the computer sends a related angle instruction to the series robot 1 and can drive the tail end of the series robot to move to a specified calibration point. The displacement sensor 9 can also be connected with a computer, and the computer can acquire the measurement data of the displacement sensor 9 in real time for data analysis.
As shown in fig. 4-5, the initial calibration device includes a closed-loop measuring device 4 and an initial calibration connecting member 13, the calibration block 6 is fixedly connected to the initial calibration connecting member 13 by using a socket head cap screw 11 and a positioning pin 12, the whole initial calibration device is fixed at a corresponding position of the closed-loop measuring device 4, each displacement sensor 9 is in planar contact with the calibration block 6 to generate a corresponding displacement, the reading of the displacement sensor 9 at this time is set to zero for use in measuring the pose of a subsequent calibration block, the calibration block 6 can be used for measuring the pose of the calibration block 6 at the tail end of a subsequent robot, and the calibration cost is saved.
The closed-loop measuring device provided by the invention measures the terminal pose of the robot by using the displacement sensors, wherein the displacement sensors comprise a displacement sensor, a laser displacement sensor, a stay wire displacement sensor and the like, the displacement sensors meeting the measurement requirements can be used for the measuring device, and the measurement precision of each sensor can reach 0.01mm or higher. The device has simple structure and low cost, is convenient to carry, and can calibrate the robot in various working environments.
Fig. 6 is a flowchart of a calibration method for stiffness of a robot joint provided by the present invention, and as shown in fig. 6, the calibration method is applied to the calibration device for stiffness of a robot joint, and the calibration method for stiffness of a robot joint includes:
step 601: and establishing a robot base coordinate system, a robot tail end coordinate system, a measurement coordinate system of a closed-loop measuring device, a calibration block coordinate system and a robot tail end load application point coordinate system.
Step 602: and initially calibrating the closed-loop measuring device by using the calibration block, and recording joint angles corresponding to a plurality of calibration points of the serial robot and the calibration displacement variation measured by a displacement sensor in the closed-loop measuring device.
The step 602 further includes, after: and determining the relative pose of the calibration block coordinate system of each calibration point relative to the measurement coordinate system by using a least square method according to the calibration displacement variation.
The determining, according to the calibration displacement variation, the relative pose of the calibration block coordinate system of each calibration point with respect to the measurement coordinate system by using a least square method specifically includes: determining a plane equation of a calibration block plane according to the serial robot under the calibration block coordinate system, and randomly selecting a position point vector on the calibration block plane, wherein a normal vector of the calibration block plane is known; converting the position point vector and the normal vector into a measurement coordinate system, and determining a plane equation of the plane equation in the measurement coordinate system according to the position point vector and the normal vector in the measurement coordinate system; bringing the pen point position coordinates of the displacement sensor into a plane equation under the measurement coordinate system, and determining a relative pose relation between the calibration displacement variation and the calibration block relative to the measurement coordinate system; establishing a pose model according to the relative pose relation; and determining the calibration relative pose of the calibration block coordinate system of each calibration point relative to the measurement coordinate system by using a least square method according to the calibration displacement variation based on the pose model.
Step 603: and replacing different mass blocks at the tail end of the series robot, applying different loads to the tail end of the series robot, driving the tail end of the series robot to reach a calibration point by utilizing the joint angle, and acquiring the current displacement variation measured by a displacement sensor in the closed-loop measuring device.
Step 604: and determining the offset generated at the tail end of the serial robot according to the calibration displacement variable quantity and the current displacement variable quantity based on the measurement coordinate system and the calibration block coordinate system.
The step 604 specifically includes: determining the current relative pose of the calibration block coordinate system of each calibration point relative to the measurement coordinate system by using the pose model and a least square method according to the current displacement variation; and determining the offset generated by the tail end of the tandem robot according to the current relative pose and the calibrated relative pose.
Step 605: and calibrating the actual joint stiffness of the series robot according to the joint angle, the offset generated by the tail end of the series robot and the force or moment borne by the tail end of the series robot under different loads based on the robot base coordinate system, the robot tail end coordinate system, the calibration block coordinate system and the robot tail end applied load point coordinate system.
The step 605 specifically includes: converting the offset generated at the tail end of the series robot and the force or moment borne by the tail end of the series robot under different loads into a robot base coordinate system; and calibrating the actual joint stiffness of the series robot by using the joint angle, the offset generated by the tail end of the series robot under the robot base coordinate system and the force or moment born by the tail end of the series robot under different loads.
The step 605 further includes: and compensating joint angular deformation of the series robot by using the actual joint stiffness.
The method and the device provided by the invention are suitable for the robot under the condition that the actual joint stiffness parameter is unknown, the actual joint stiffness parameter is obtained by calibrating the joint stiffness of the robot, and the joint angular deformation of the robot is compensated to improve the absolute positioning precision of the robot. The closed-loop measuring device provided by the invention has no requirement on the use environment, can be used for calibrating the joint stiffness in various working occasions, and has a simple structure and a very simple operation process.
As an optional implementation manner of the present invention, a method for calibrating the stiffness of a robot joint, as shown in fig. 7, includes the following specific steps:
step 100: and after the experimental equipment is installed, establishing a related coordinate system, and initially calibrating the closed-loop measuring device by using the initial calibration device. So that the reading of each displacement sensor in the closed-loop measuring device is set to be zero under the condition of initial calibration.
Specifically, the structural schematic diagram of the initial calibration is shown in fig. 4-5, and includes a closed-loop measuring device 4, a clamping plate bracket 5, a calibration block 6, a displacement sensor 9, an initial calibration connecting member 13, a socket head cap screw 11 and a positioning pin 12. The basic process is as follows: the initial calibration device is composed of a closed loop measuring device 4 and an initial calibration connecting piece 13. The calibration block 6 is fixedly connected with the initial calibration connecting piece 13 by using the socket head cap screws 11 and the positioning pins 12, and the whole initial calibration device is fixed on the corresponding position of the closed-loop measuring device 4. Each displacement sensor 9 is in plane contact with the calibration block 6 to generate a corresponding displacement, and the reading of the displacement sensor 9 at the moment is set to be zero, so that the subsequent calibration block pose measurement can be carried out. The calibration block 6 can be used for measuring the pose of the calibration block 6 at the tail end of the subsequent robot, so that the calibration cost is saved.
Step 200: installing a calibration block for initial calibration on a robot end connecting piece for position and attitude measurement, manually teaching the robot, keeping the calibration block on the robot end connecting piece in contact with a displacement sensor in a closed-loop measuring device, and recording joint angles q corresponding to N points for manual teachingN(N ═ 1, 2, 3.., N) and the displacement E of the displacement sensorN(N＝1，2，3，...，n)。
Specifically, the displacement sensor measures the obtained data EN∈R6×1Wherein E isN＝[e1，e2，e3，e4，e5，e6]FIndicating the amount of displacement measured by each displacement sensor. Displacement variation E obtained by collectionNCalculating the coordinate system { O } of each calibration point by least square methodMXMYMZMRelative to a measurement coordinate system OCXCYCZCRelative pose of }
Wherein the content of the first and second substances,
the column vector of (a) is,
[x，y，z]Tthe position of the coordinate system of the calibration block relative to the directions of the x axis, the y axis and the z axis of the coordinate system of the measurement is represented; [ alpha, beta, gamma ]]TThe angles (attitudes) of the calibration block coordinate system with respect to the x-axis, y-axis, and z-axis directions of the measurement coordinate system are indicated.
Further, a calibration block pose measurement algorithm flow based on a six-point positioning principle is shown in fig. 8, a robot tail end calibration block pose measurement principle is shown in fig. 9, a mathematical model of the displacement variation of a displacement sensor and the pose relation of a calibration block relative to a measurement coordinate system is established, and a least square method is used for calculation to obtain the position of the calibration block
The method comprises the following specific steps:
step 210: in a calibration block coordinate system { O }MXMYMZMObtaining a calibration block plane by a mechanical structureMS1The plane equation of (1) randomly selecting a position point vector on the planeMH1Knowing the normal vector of the planeMK1；
Step 220: the position point vector in the step 210 is calculatedMH1Sum normal vectorMK1Converting the coordinate system to a measurement coordinate system { O }CXCYCZCThe following steps:
CS1plane in measurement coordinate system { OCXCYCZCEquation of the plane under }Comprises the following steps:
step 230: in the measurement coordinate system { OCXCYCZCAt this time, the pen point position coordinates of the displacement sensor are knownCP1Bring it into the plane equationCS1To obtain the sensor displacement e1And the relative pose of the calibration block relative to the measurement coordinate system.
Step 240: integrating the relationship equations of other displacement amounts in step 230 to obtain a mathematical model, and solving by a least square algorithm to obtain a relative pose Xi(ii) a Wherein E isiThe displacement variation of the six displacement sensors.
Xi＝f(Ei) (7)
Step 300: adding different masses M to the robot end connection within the rated load of the robotiThe mass of (2). Reusing the joint angle q in step 200NThe tail end of the driving robot reaches the calibration point and records the displacement of the displacement sensor
Specifically, the robot tip is subjected to load and generates joint angular deformation, so that the robot tip is shifted by Δ X, and the displacement of the displacement sensor is changed
Calculating a calibration block coordinate system (O) of the calibration point by a least square methodMXMYMZMRelative to a measurement coordinate system OCXCYCZCRelative pose of }
Obtaining the offset generated at the tail end of the robot under each group of different load experiments:
wherein the content of the first and second substances,
the column vector of (a) is,
indicating the position and angular (attitude) offset of the calibration block coordinate system with respect to the x-, y-, z-axis directions of the measurement coordinate system. Mass block MiThe force generated to the tail end of the robot can be measured by a known mechanical structure and a closed-loop measuring device to obtain the relative pose relationship
Is calculated to obtain Fi. Wherein, Fi＝[fx，fy，fz，nx，ny，nz]TRepresenting x-axis, y-axis, z-axis forces and moments on the robot tip.
Further, the mass M of the mass blockiShould be controlled within the robot end payload. Force F generated by load point applied to tail end of robot by mass blocki＝Mig, wherein g ∈ R3×1Is the gravitational acceleration direction. g can be calculated by mechanical structure and coordinate system conversion: the direction g of the gravitational acceleration is a coordinate system transformation matrix
Of the z-axis direction vector of (a), wherein,
coordinate system of robot end load application point { O }FXFYFZFRelative to a measurement coordinate system (O)CXCYCZCConverting a matrix by a coordinate system; because the gravity of the mass passes the coordinates of the point of application of the loadIs { O }FXFYFZFThe origin of the mass, the gravity of the mass generates zero moment for the coordinate system.
Step 400: according to the collected multiple groups of joint angles qNAnd each group of different loads MiOffset generated by robot end under experiment
And each set of different loads MiForce F borne by tail end of robot 1 in experimentiCalibrating actual joint stiffness parameter K of robotq：
Wherein the end of the robot is subjected to a force FiAnd offset generated by robot end
Requires conversion of the coordinate system to the robot base coordinate system { O }BXBYBZBAnd (6) below.
Coordinate system (O) representing load point applied to robot endFXFYFZFRelative to the robot base coordinate system { O }BXBYBZBForce and moment of { C };
coordinate system of calibration block (O) representing robot endMXMYMZMRelative to the robot base coordinate system { O }BXBYBZBPose offset of }; j. the design is a squareq∈R6×6Is a robot kinematics jacobian matrix. KqJoint stiffness parameters to be calibrated for the robot: kq＝diag(kq1，kq2，kq3，kq4，kq5，kq6). Calculating through multiple groups of experimental data, and calculating the actual joint stiffness parameter K of the robot by using a least square methodqAnd completing calibration. Then using the actual joint stiffness parameter KqThe angular deformation of the joint of the robot is compensated to improve the absolute positioning precision of the robot:
wherein Q isiActual joint angles of the experimental calibration points of each group are calculated; q. q.siNominal joint angles for each set of experimental calibration points; tau isiAnd robot joint torque of each group of experimental calibration points.
Specifically, since the robot jacobian matrix is the kinematic change of the robot end coordinate system relative to the robot base coordinate system, the measurement calculation yields the end force FiAnd end offset
Requires conversion of the coordinate system to the robot base coordinate system { O }BXBYBZBAnd (6) carrying out calibration calculation:
wherein R ∈ R3×3Is a rotation matrix of the coordinate system transformation matrix T; p is epsilon of R3×1Is the position vector of the coordinate system transformation matrix T, p ═ px，py，pz]T(ii) a S (p) is defined as the antisymmetric matrix of the position vector p. For robot joint momentTau is measured, and joint torque can be measured and read by a general robot through a built-in joint torque sensor; some robots can calculate joint moments by measuring their current loops.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other.
The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.
Claims (9)
1. A calibration device for robot joint rigidity is characterized by comprising: the system comprises a serial robot, an inclined plane base, an experiment platform, a closed loop measuring device, a tail end connecting piece and a clamping plate bracket;
the inclined plane base and the clamping plate bracket are arranged on the experiment platform; the series robot is arranged on the inclined plane base, a mass block is arranged between the tail end of the series robot and the closed-loop measuring device, and the mass block is used for applying load to the tail end of the series robot; the closed-loop measuring device is supported by the splint support, a calibration block is arranged in the closed-loop measuring device and used for calibrating the tail end of the serial robot, and the closed-loop measuring device is used for calibrating the joint rigidity of the serial robot; the end connecting piece is used for connecting the serial robot and the calibration block; the mass block is arranged between the tail end of the serial robot and the tail end connecting piece.
2. The calibration device for the stiffness of the robot joint according to claim 1, wherein the closed-loop measuring device specifically comprises: the clamp plate group, the displacement sensor, the inner hexagon screw, the positioning pin and the movable plate;
the clamping plate group comprises three clamping plates, and every two adjacent virtual cubes are formed by the three clamping plates; the movable plate is arranged on any side surface of the virtual cube;
each clamping plate is provided with the displacement sensor; each displacement sensor is in contact with the plane of the calibration block and is used for measuring the displacement variation of the movement of the calibration block;
the inner hexagonal screw and the positioning pin are arranged on the movable plate, and the movable plate is used for driving the calibration block to move.
3. The calibration device for the rigidity of the robot joint according to claim 2, further comprising: initially calibrating a connecting piece;
the initial calibration connecting piece is arranged on the movable plate and fixedly connected with the initial calibration connecting piece and the calibration block through the inner hexagonal screw and the positioning pin.
4. A calibration method for robot joint stiffness is characterized in that the calibration method is applied to a calibration device for robot joint stiffness, and the calibration device for robot joint stiffness comprises the following steps: the system comprises a serial robot, an inclined plane base, an experiment platform, a closed loop measuring device, a tail end connecting piece and a clamping plate bracket; the inclined plane base and the clamping plate bracket are arranged on the experiment platform; the series robot is arranged on the inclined plane base, a mass block is arranged between the tail end of the series robot and the closed-loop measuring device, and the mass block is used for applying load to the tail end of the series robot; the closed-loop measuring device is supported by the splint support, a calibration block is arranged in the closed-loop measuring device and used for calibrating the tail end of the serial robot, and the closed-loop measuring device is used for calibrating the joint rigidity of the serial robot; the end connecting piece is used for connecting the serial robot and the calibration block; the mass block is arranged between the tail end of the serial robot and the tail end connecting piece;
the calibration method of the robot joint stiffness comprises the following steps:
establishing a robot base coordinate system, a robot tail end coordinate system, a measurement coordinate system of a closed-loop measuring device, a calibration block coordinate system and a robot tail end load application point coordinate system;
the calibration block is utilized to perform initial calibration on the closed-loop measuring device, and joint angles corresponding to a plurality of calibration points of the serial robot and calibration displacement variation measured by a displacement sensor in the closed-loop measuring device are recorded;
replacing different mass blocks at the tail end of the series robot, applying different loads to the tail end of the series robot, driving the tail end of the series robot to reach a calibration point by utilizing the joint angle, and acquiring the current displacement variation measured by a displacement sensor in the closed-loop measuring device;
determining the offset generated at the tail end of the serial robot according to the calibration displacement variable quantity and the current displacement variable quantity based on the measurement coordinate system and the calibration block coordinate system;
and calibrating the actual joint stiffness of the series robot according to the joint angle, the offset generated by the tail end of the series robot and the force or moment borne by the tail end of the series robot under different loads based on the robot base coordinate system, the robot tail end coordinate system, the calibration block coordinate system and the robot tail end applied load point coordinate system.
5. The method for calibrating the rigidity of the robot joint according to claim 4, wherein the initially calibrating the closed-loop measuring device by the calibration block, recording the joint angles corresponding to a plurality of calibration points of the serial robot and the variation of the calibrated displacement measured by the displacement sensor in the closed-loop measuring device, and then further comprising:
and determining the relative pose of the calibration block coordinate system of each calibration point relative to the measurement coordinate system by using a least square method according to the calibration displacement variation.
6. The method for calibrating the rigidity of the robot joint according to claim 5, wherein the determining the relative pose of the calibration block coordinate system of each calibration point with respect to the measurement coordinate system by using a least square method according to the calibration displacement variation specifically comprises:
determining a plane equation of a calibration block plane according to the serial robot under the calibration block coordinate system, and randomly selecting a position point vector on the calibration block plane, wherein a normal vector of the calibration block plane is known;
converting the position point vector and the normal vector into a measurement coordinate system, and determining a plane equation of the plane equation in the measurement coordinate system according to the position point vector and the normal vector in the measurement coordinate system;
bringing the pen point position coordinates of the displacement sensor into a plane equation under the measurement coordinate system, and determining a relative pose relation between the calibration displacement variation and the calibration block relative to the measurement coordinate system;
establishing a pose model according to the relative pose relation;
and determining the calibration relative pose of the calibration block coordinate system of each calibration point relative to the measurement coordinate system by using a least square method according to the calibration displacement variation based on the pose model.
7. The method for calibrating joint stiffness of a robot according to claim 6, wherein the determining an offset generated at an end of the tandem robot according to the calibrated displacement variation and the current displacement variation based on the measured coordinate system and the calibrated block coordinate system specifically comprises:
determining the current relative pose of the calibration block coordinate system of each calibration point relative to the measurement coordinate system by using the pose model and a least square method according to the current displacement variation;
and determining the offset generated by the tail end of the tandem robot according to the current relative pose and the calibrated relative pose.
8. The method for calibrating the rigidity of the robot joint according to claim 4, wherein the calibrating the actual joint rigidity of the tandem robot according to the joint angle, the offset generated by the tail end of the tandem robot, and the force or the moment borne by the tail end of the tandem robot under different loads based on the robot base coordinate system, the robot tail end coordinate system, the calibration block coordinate system, and the robot tail end load application point coordinate system specifically comprises:
converting the offset generated at the tail end of the series robot and the force or moment borne by the tail end of the series robot under different loads into a robot base coordinate system;
and calibrating the actual joint stiffness of the series robot by using the joint angle, the offset generated by the tail end of the series robot under the robot base coordinate system and the force or moment born by the tail end of the series robot under different loads.
9. The method for calibrating the rigidity of the robot joint according to claim 4, wherein the method for calibrating the actual joint rigidity of the tandem robot according to the joint angle, the offset generated by the tail end of the tandem robot, and the force or moment borne by the tail end of the tandem robot under different loads based on the robot base coordinate system, the robot tail end coordinate system, the calibration block coordinate system, and the robot tail end load application point coordinate system further comprises:
and compensating joint angular deformation of the series robot by using the actual joint stiffness.
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