CN111531533A - Zero point correction and gravity compensation method for six-dimensional force sensor - Google Patents

Zero point correction and gravity compensation method for six-dimensional force sensor Download PDF

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Publication number
CN111531533A
CN111531533A CN202010291451.0A CN202010291451A CN111531533A CN 111531533 A CN111531533 A CN 111531533A CN 202010291451 A CN202010291451 A CN 202010291451A CN 111531533 A CN111531533 A CN 111531533A
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robot
gravity compensation
zero
force sensor
dimensional force
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Inventor
管贻生
陈浩文
李坚
王兵
张涛
杨宇峰
蔡传武
张宏
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Foshan Biowin Robotics And Automation Co ltd
Guangdong University of Technology
Foshan Nanhai Guangdong Technology University CNC Equipment Cooperative Innovation Institute
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Foshan Biowin Robotics And Automation Co ltd
Guangdong University of Technology
Foshan Nanhai Guangdong Technology University CNC Equipment Cooperative Innovation Institute
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
    • B25J—MANIPULATORS; CHAMBERS PROVIDED WITH MANIPULATION DEVICES
    • B25J9/00—Programme-controlled manipulators
    • B25J9/16—Programme controls
    • B25J9/1628—Programme controls characterised by the control loop
    • B25J9/1633—Programme controls characterised by the control loop compliant, force, torque control, e.g. combined with position control
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
    • B25J—MANIPULATORS; CHAMBERS PROVIDED WITH MANIPULATION DEVICES
    • B25J13/00—Controls for manipulators
    • B25J13/08—Controls for manipulators by means of sensing devices, e.g. viewing or touching devices
    • B25J13/085—Force or torque sensors
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
    • B25J—MANIPULATORS; CHAMBERS PROVIDED WITH MANIPULATION DEVICES
    • B25J9/00—Programme-controlled manipulators
    • B25J9/16—Programme controls
    • B25J9/1628—Programme controls characterised by the control loop
    • B25J9/1638—Programme controls characterised by the control loop compensation for arm bending/inertia, pay load weight/inertia
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
    • B25J—MANIPULATORS; CHAMBERS PROVIDED WITH MANIPULATION DEVICES
    • B25J9/00—Programme-controlled manipulators
    • B25J9/16—Programme controls
    • B25J9/1679—Programme controls characterised by the tasks executed
    • B25J9/1692—Calibration of manipulator

Abstract

The invention discloses a zero point correction and gravity compensation method of a six-dimensional force sensor, which mainly comprises the following two processes: (1) zero point correction and gravity compensation parameter solution; (2) zero point correction and gravity compensation. In application scenes such as polishing of the robot, man-machine interaction of a cooperative robot and the like, the robot needs to accurately sense the stress state of the end effector, and the invention can be used for carrying out zero correction and gravity compensation on a six-dimensional force sensor arranged between the tail end of the robot and the end effector and provides a technical basis for contact force sensing of the robot. The invention simultaneously considers the zero drift problem of the sensor and the installation error of the robot, simultaneously carries out zero correction and gravity compensation on the six-dimensional force sensor, and has no requirements on the installation of the end effector and the robot in the solving process, so compared with the traditional gravity compensation method, the invention has the advantages of higher precision and simple and convenient operation.

Description

Zero point correction and gravity compensation method for six-dimensional force sensor
Technical Field
The invention relates to the technical field of robots, in particular to a zero point correction and gravity compensation method for a six-dimensional force sensor for robot contact force sensing.
Background
The robot and the intelligent manufacturing technology are the necessary routes from the 'manufacturing big country' to the 'manufacturing strong country' in China, and become the leading research hotspots of the manufacturing subject. Robots are being used more and more in the manufacturing industry, and at the same time, the interaction scene of human and robot is being more and more involved in the process of wide application. On the premise, in some application scenarios, the robot needs to accurately sense the contact force at the tail end, such as:
1) industrial robots are used for contact operations such as polishing and sanding. In such a contact-type working environment, in order to avoid excessive or insufficient polishing, it is necessary for the robot to accurately sense the contact force of the polishing tool at the end thereof and control the contact force between the polishing tool and the surface of the workpiece. Further, when the robot polishes a complex curved surface workpiece, in order to enable the end polishing tool to be adaptive to the surface of the workpiece, it is necessary to estimate the contact state between the polishing tool and the workpiece according to the end contact force.
2) And (3) the cooperative robot and the human carry out an interaction process. Under the operation condition that the robot and the human coexist, in order to ensure safety and enable the robot to show certain flexibility, the contact force of the tail end of the robot is often required to be sensed, and some safety protection mechanisms and flexibility control are realized.
In order to enable the robot to have the capability of contact force sensing, two schemes are provided, namely, a torque sensor is arranged at each joint of the robot (or a double encoder is arranged, or the torque is estimated through current); firstly, a six-dimensional force sensor is arranged at the tail end of the robot. However, whatever means is used to measure, estimate and calculate the end-contact force, the obtained measurement value is affected by the gravity of the robot end-effector (and the dead weight of each joint of the robot for the solution in which the sensor is installed at each joint), and in order to accurately obtain the contact force of the tool end, it is necessary to perform gravity compensation on the measurement value while the robot is in any pose to eliminate the influence of the end-effector gravity from the measurement value. In the case of the arrangement using the force sensor, the zero point of the force sensor is also affected by factors such as the ambient temperature, the mounting preload, and the self weight of the sensor, and the zero point correction of the sensor is also required because the zero point of the force sensor is shifted and the measurement result is greatly affected.
In the existing method for carrying out zero point correction and gravity compensation on a six-dimensional force sensor installed at the tail end of a robot, the zero point drift problem of the sensor is not considered in some methods, and the zero point of the sensor needs to be obtained by other methods before compensation; some robots do not consider installation errors, and assume that a robot coordinate system is overlapped with a world coordinate system; some methods need to repeatedly measure the robot in a specific pose in the process of solving the compensation parameters, and are complex in steps and prone to errors. Accordingly, further improvements and improvements are needed in the art.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a zero point correction and gravity compensation method of a six-dimensional force sensor, which is convenient to operate and high in precision.
The purpose of the invention is realized by the following technical scheme:
a zero point correction and gravity compensation method for a six-dimensional force sensor mainly comprises the following steps:
step S1: zero point correction and gravity compensation parameter solution;
step S2: zero point correction and gravity compensation;
the zero point correction is performed simultaneously with the gravity compensation.
As a preferred embodiment of the present invention, the zero point correction and gravity compensation parameters in step S1 include: zero drift value F of force component of six-dimensional force sensor0(ii) a Zero drift value T of moment component of six-dimensional force sensor0(ii) a Coordinates of gravity under robot base coordinate systemBG; and (3) the coordinate l of the center of gravity of the end effector under the sensor coordinate system.
As a preferred embodiment of the present invention, the zero point calibration and gravity compensation parameters in step S1 may be calculated and obtained at a time after recording and obtaining required data, where the required data includes rotation transformation of the robot end relative to the robot base system and the reading of the six-dimensional force sensor when the robot is in different postures.
Further, the step S1 further includes the following steps:
step S11: moving the robot to a proper initial pose;
step S12: keeping the position of the tail end of the robot unchanged, randomly selecting the posture of the tail end of the robot, and moving the robot to the posture;
step S13: reading the current attitude of the tail end of the robot from the robot controller;
step S14: reading a sensor reading in the current robot posture from a six-dimensional force sensor;
step S15: judging whether the number of the currently recorded data groups is more than or equal to 3 groups, if so, repeating the step S12-the step S14, and otherwise, entering the next step;
step S16: calculating zero correction and gravity compensation parameters: coordinates of gravity under robot base coordinate systemBG and sixZero drift value F of force component of dimensional force sensor0；
Step S17: calculating zero correction and gravity compensation parameters: coordinate l of center of gravity of end effector under sensor standard coordinate system and zero drift value T of moment component of six-dimensional force sensor0；
Step S18: determining the zero point calibration and gravity compensation parameter F calculated in the steps S16 and S170、T0、l、BG, whether the precision requirement is met or not is judged, if the precision requirement is not met, the steps S12-S17 are repeated until the precision requirement is met;
step S19: and storing the obtained zero point correction and gravity compensation parameters on a storage medium.
As a preferred embodiment of the present invention, in step S14, the sensor reading from the six-dimensional force sensor includes a force component F and a moment component T, and the force component and the moment component each include values in three directions of x, y, and z.
As a preferable aspect of the present invention, the determination of whether the required accuracy is achieved in step S18 may be calculated by the following error formula:
Figure BDA0002450544620000031
Figure BDA0002450544620000032
wherein the content of the first and second substances,
Figure BDA0002450544620000033
for the robot pose recorded in step S13, Fi、TiForce component, moment component, F, respectively, of the six-dimensional force sensor reading recorded in step S140、T0、BG. l are respectively zero correction and gravity compensation parameters: the zero drift value of the force component of the six-dimensional force sensor, the zero drift value of the moment component of the six-dimensional force sensor, the coordinate of the gravity under a robot base coordinate system and the coordinate of the gravity center of the end effector under a sensor coordinate system.
Further, the step S2 further includes the following steps:
step S21: loading the zero point correction and gravity compensation parameters saved in the step S1 from the storage medium;
step S22: reading the current attitude of the tail end of the robot from the robot controller;
step S23: reading a sensor reading in the current robot posture from a six-dimensional force sensor;
step S24: performing zero correction and gravity compensation on the sensor reading according to the zero correction and gravity compensation parameters obtained by the step S1;
step S25: and judging whether zero point correction and gravity compensation are needed, if so, repeating the step S22 to the step S25, and if not, exiting the zero point correction and gravity compensation process.
In a preferred embodiment of the present invention, in step S22, the sensor readings from the six-dimensional force sensor include a force component F and a moment component T, each of which includes values in three directions x, y, and z.
As a preferred embodiment of the present invention, in step S3, the zero point correction and gravity compensation for the sensor reading can be calculated by the following formulas:
Figure BDA0002450544620000041
Figure BDA0002450544620000042
wherein, Fr、TrRespectively the force and the moment born by the end effector after compensation, F, T respectively the force and the moment components of the measured value of the six-dimensional force sensor, F0、T0、BG. l is the zero drift value of the force component of the six-dimensional force sensor, the zero drift value of the moment component of the six-dimensional force sensor, the coordinate of the gravity under the robot base coordinate system and the coordinate of the gravity center of the end effector under the sensor coordinate system, which are obtained by the solution in the step S1.
Compared with the prior art, the invention also has the following advantages: the invention simultaneously considers the installation error of the robot and the zero drift of the force sensor, only needs to measure the original data of the force sensor under several random robot poses, can obtain all parameters for zero correction and gravity compensation at one time through calculation, and then can carry out zero correction and gravity compensation on the measured data of the six-dimensional force sensor under any robot pose.
Drawings
Fig. 1 is a schematic view of the robot, force sensor and end effector assembly provided by the present invention.
FIG. 2 is a flow chart of the zero point correction and gravity compensation parameter solving process provided by the present invention.
FIG. 3 is a flow chart of the zero point calibration and gravity compensation process provided by the present invention.
The reference numerals in the above figures illustrate:
1-six-dimensional force sensor, 2-end actuator, 3-sensor coordinate system, 4-end actuator gravity center, 5-end actuator gravity, 6-end actuator gravity coordinate under base coordinate system, 7-robot base coordinate system, 8-installation inclination angle, 9-robot.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer and clearer, the present invention is further described below with reference to the accompanying drawings and examples.
Example 1:
as shown in fig. 1 to 3, the present embodiment discloses a zero point calibration and gravity compensation method for a six-dimensional force sensor, which mainly includes the following steps:
step S1: zero point correction and gravity compensation parameter solution;
step S2: zero point correction and gravity compensation;
the zero point correction is performed simultaneously with the gravity compensation.
As a preferred embodiment of the present invention, the zero point correction and gravity compensation parameters in step S1 include: six-dimensional force sensor forceZero drift value F of the component0(ii) a Zero drift value T of moment component of six-dimensional force sensor0(ii) a Coordinates of gravity under robot base coordinate systemBG; and (3) the coordinate l of the center of gravity of the end effector under the sensor coordinate system.
As a preferred embodiment of the present invention, the zero point calibration and gravity compensation parameters in step S1 may be calculated and obtained at a time after recording and obtaining required data, where the required data includes rotation transformation of the robot end relative to the robot base system and the reading of the six-dimensional force sensor when the robot is in different postures.
Further, the step S1 further includes the following steps:
step S11: moving the robot to a proper initial pose;
step S12: keeping the position of the tail end of the robot unchanged, randomly selecting the posture of the tail end of the robot, and moving the robot to the posture;
step S13: reading the current attitude of the tail end of the robot from the robot controller;
step S14: reading a sensor reading in the current robot posture from a six-dimensional force sensor;
step S15: judging whether the number of the currently recorded data groups is more than or equal to 3 groups, if so, repeating the step S12-the step S14, and otherwise, entering the next step;
step S16: calculating zero correction and gravity compensation parameters: coordinates of gravity under robot base coordinate systemBZero drift value F of force component of G and six-dimensional force sensor0；
Step S17: calculating zero correction and gravity compensation parameters: coordinate l of center of gravity of end effector under sensor standard coordinate system and zero drift value T of moment component of six-dimensional force sensor0；
Step S18: determining the zero point calibration and gravity compensation parameter F calculated in the steps S16 and S170、T0、l、BG meets the precision requirement, if not, the step S12E is repeatedStep S17, until reaching the precision requirement;
step S19: and storing the obtained zero point correction and gravity compensation parameters on a storage medium.
As a preferred embodiment of the present invention, in step S14, the sensor reading from the six-dimensional force sensor includes a force component F and a moment component T, and the force component and the moment component each include values in three directions of x, y, and z.
As a preferable aspect of the present invention, the determination of whether the required accuracy is achieved in step S18 may be calculated by the following error formula:
Figure BDA0002450544620000061
Figure BDA0002450544620000062
wherein the content of the first and second substances,
Figure BDA0002450544620000063
for the robot pose recorded in step S13, Fi、TiForce component, moment component, F, respectively, of the six-dimensional force sensor reading recorded in step S140、T0、BG. l are respectively zero correction and gravity compensation parameters: the zero drift value of the force component of the six-dimensional force sensor, the zero drift value of the moment component of the six-dimensional force sensor, the coordinate of the gravity under a robot base coordinate system and the coordinate of the gravity center of the end effector under a sensor coordinate system.
Further, the step S2 further includes the following steps:
step S21: loading the zero point correction and gravity compensation parameters saved in the step S1 from the storage medium;
step S22: reading the current attitude of the tail end of the robot from the robot controller;
step S23: reading a sensor reading in the current robot posture from a six-dimensional force sensor;
step S24: performing zero correction and gravity compensation on the sensor reading according to the zero correction and gravity compensation parameters obtained by the step S1;
step S25: and judging whether zero point correction and gravity compensation are needed, if so, repeating the step S22 to the step S25, and if not, exiting the zero point correction and gravity compensation process.
In a preferred embodiment of the present invention, in step S22, the sensor readings from the six-dimensional force sensor include a force component F and a moment component T, each of which includes values in three directions x, y, and z.
As a preferred embodiment of the present invention, in step S3, the zero point correction and gravity compensation for the sensor reading can be calculated by the following formulas:
Figure BDA0002450544620000064
Figure BDA0002450544620000065
wherein, Fr、TrRespectively the force and the moment born by the end effector after compensation, F, T respectively the force and the moment components of the measured value of the six-dimensional force sensor, F0、T0、BG. l is the zero drift value of the force component of the six-dimensional force sensor, the zero drift value of the moment component of the six-dimensional force sensor, the coordinate of the gravity under the robot base coordinate system and the coordinate of the gravity center of the end effector under the sensor coordinate system, which are obtained by the solution in the step S1.
Example 2:
the embodiment discloses a zero point correction and gravity compensation method of a six-dimensional force sensor, which comprises the following processes:
(1) zero point correction and gravity compensation parameter solution;
(2) zero point correction and gravity compensation.
To explain the above-mentioned zero point correction and gravity compensation parameter solving process in detail, the zero point correction and gravity compensation are explained in principle. As shown in fig. 1, a six-dimensional force sensor 1 is installed between the end of a robot 9 and an end effector 2, a robot base coordinate system 7 is fixed on a robot base, the gravity direction is not on the z-axis of the robot base coordinate system due to possible installation errors of the robot, an installation inclination angle 8 is generated, a sensor coordinate system 3 is fixed on the sensor, and an end effector gravity 5 acts on an end effector gravity center 4. For an end effector mounted at the end of a robot, the purpose of zero point correction and gravity compensation is to subtract the zero point drift value of the sensor and the gravity and gravity moment of the end effector from the measured value of the six-dimensional force sensor. Accordingly, the following equations may be listed:
Fr＝F-F0-SG (1)
Tr＝T-T0-l×SG (2)
Figure BDA0002450544620000071
in the formula Fr、TrRepresenting the external force and external moment applied to the end effector under the sensor coordinate system, F, T representing the force and moment measured by the sensor, F0、T0The zero drift values of the sensor force and the sensor moment are expressed, l represents the coordinate of the gravity center of the end effector under a sensor coordinate system,SG、Bg respectively represents the coordinates of gravity in a sensor coordinate system and a robot base coordinate system,
Figure BDA0002450544620000072
representing a rotational transformation of the sensor coordinate system with respect to the robot base coordinate system. The relative relationship among the coordinates, coordinate system, gravity, etc. is shown in fig. 1.
From the above equation, it can be seen that the zero point correction and gravity compensation for the end effector only need to obtain the parameter F0、T0L andBg, the parameters are called zero point correction and gravity compensation in the invention.
In order to solve the zero point correction and the gravity compensation parameters, it is assumed that the end effector mounted at the end of the robot is only acted by gravity and not by any other external force, and then the equations (1) and (2) can be simplified as follows:
F-F0-SG＝0 (4)
T-T0-l×SG＝0 (5)
transforming equation (3) yields:
Figure BDA0002450544620000081
substituting into formula (4) to obtain
Figure BDA0002450544620000082
Wherein, I3Representing a three-dimensional unit matrix, and recording the force component of the measurement value of the six-dimensional force sensor and the posture of the tail end of the robot by n supposing that the force component and the posture are respectively marked as F under different robot postures1,F2,…,FnAnd
Figure BDA0002450544620000083
the following set of equations may be listed:
Figure BDA0002450544620000084
the n different robot poses are required to ensure that the formula (8) can form at least 6 linearly independent equations. Let equation (8) be:
f＝Ag (9)
where f is a 3 n-dimensional column vector, a is a matrix of 3n × 6 in shape, and g is a 6-dimensional column vector.
Left-hand multiplying formula (9) by ATThen, multiply left by (A)TA)-1Obtaining:
g＝(ATA)-1ATf (10)
g, i.e. the base coordinate of gravity in the zero point correction and gravity compensation parameters, can be obtainedBZero drift value F of coordinate and six-dimensional force sensor force component under G system0。
By shifting the term of equation (5), the transformation can be:
T＝l×SG+T0(11)
wherein the content of the first and second substances,SG＝[gxgygz]Tthe vector cross product in equation (11) is now transformed into a matrix multiplication, which can be found from equation (6), such that:
Figure BDA0002450544620000085
equation (11) can be transformed into:
Figure BDA0002450544620000086
assuming that under n different robot poses, this n pose is recorded, it will beBG is converted into a sensor coordinate system and is converted into a matrix form according to a formula (12), and the matrix form is marked as M1,M2,…,MnRecording the moment component of the measured value of the six-dimensional force sensor, denoted as T1,T2,…,TnThen the following set of equations can be listed:
Figure BDA0002450544620000091
the n different robot poses are required to ensure that the formula (14) can form at least 6 linearly independent equations. Let equation (14) be:
t＝Bh (15)
where t is a 3 n-dimensional column vector, B is a matrix of 3n × 6 in shape, and h is a 6-dimensional column vector.
Left-multiplying equation (15) by BTThen multiply to the left (B)TB)-1Obtaining:
h＝(BTB)-1BTt (16)
then h is found, i.e. end executionCoordinate l of gravity center of the device under sensor coordinate system and zero drift value T of moment component of six-dimensional force sensor0. All zero point calibration and gravity compensation parameters have been obtained.
The zero point calibration and gravity compensation process can be described in detail as follows. And carrying out zero correction and gravity compensation on the six-dimensional force sensor of the robot in a certain position.
The above-mentioned certain posture can be arbitrary in the working space of robot, and its posture can be recorded asSBR, i.e. the rotational transformation of the sensor coordinate system with respect to the robot base coordinate system.
The rotational transformation of the sensor coordinate system with respect to the robot base coordinate system can be typically from the robot controller rotation angle A, B, C, or quaternion qw、qx、qy、qzAnd converting the matrix into a rotation matrix.
The gravity under the robot base coordinate system can be converted according to the rotation of the sensor coordinate system relative to the robot base coordinate systemBG is transformed to the sensor coordinate system by the following formula:
Figure BDA0002450544620000092
when the robot is in the above-described attitude, the measured values are read from the six-dimensional force sensor, the force component of the measured values is denoted as F, and the moment component of the measured values is denoted as T. The real value after zero point correction and gravity compensation can be obtained by the following formula:
Fr＝F-F0-SG (18)
Tr＝T-T0-l×SG (19)
wherein, Fr、TrThe real values of the stress and the moment of the end effector after zero point correction and gravity compensation are respectively F0、T0L is zero drift value of force component of six-dimensional force sensor, zero drift value of moment component and center of gravity of end effector in the zero correction and gravity compensation parametersCoordinates in the sensor coordinate system.
Example 3:
the embodiment discloses a zero point correction and gravity compensation method for a six-dimensional force sensor, as shown in fig. 1, zero point correction and gravity compensation are performed on the six-dimensional force sensor in the figure, and firstly, zero point correction and gravity compensation parameters are solved. Fig. 2 shows a flowchart of the zero point correction and gravity compensation parameter solving process. Referring to fig. 2, the process of solving the zero point correction and gravity compensation parameters in this embodiment includes:
s1: moving the robot to a proper initial pose;
s2: keeping the position of the tail end of the robot unchanged, randomly selecting the posture of the tail end of the robot, and moving the robot to the posture;
s3: the current robot end attitude is read from the robot controller, and in this embodiment, the robot end attitude is given in the form of a quaternion, denoted as qwi、qxi、qyi、qziThe subscript is the data number of the current record, and the quaternion is converted into the form of a rotation matrix according to the following formula:
Figure BDA0002450544620000101
s4: reading the sensor reading in the current robot posture from the six-dimensional force sensor, and recording the force component of the sensor reading as FiThe moment component is denoted as TiSubscript i is the data number of the current record;
s5: judging whether the number of the currently recorded data groups is more than or equal to 3 groups, if so, repeating the steps from S2 to S4, otherwise, performing the next step;
s6: calculating zero correction and gravity compensation parameters: the zero drift values of the gravity in the coordinates of the robot base coordinate system and the force component of the six-dimensional force sensor record the rotation matrix in each group of dataSBRiAnd a three-dimensional identity matrix I3Performing matrix splicing as follows, and recording as a matrix A:
Figure BDA0002450544620000102
force component F of six-dimensional force sensor measurement values in each recorded group of dataiThe following concatenation is performed, denoted vector f:
Figure BDA0002450544620000103
a, f was calculated as follows, and the result was recorded as g:
g＝(ATA)-1ATf
the resulting calculated vector g is a 6-dimensional column vector whose first three terms areBG, the last three terms are F0；
S7: calculating zero correction and gravity compensation parameters: the zero drift value of the gravity center of the end effector in the coordinate system of the sensor and the moment component of the six-dimensional force sensor is obtained in S6BG, according to the rotation matrix in each recorded group of data
Figure BDA0002450544620000111
And transforming the sensor coordinate system into a sensor coordinate system under each posture, wherein the transformation process can be performed by the following formula:
Figure BDA0002450544620000112
g obtained from the above formulaxi、gyi、gziMatrix M spliced asi：
Figure BDA0002450544620000113
Then M is putiAnd a three-dimensional identity matrix I3Performing matrix splicing as follows, and recording as a matrix B:
Figure BDA0002450544620000114
the moment component T of the six-dimensional force sensor measurement value in each recorded group of dataiThe following concatenation is performed, denoted vector t:
Figure BDA0002450544620000115
b, t was calculated as follows, and the result was recorded as h:
h＝(BTB)-1BTt
the obtained calculation result vector h is a 6-dimensional column vector, the first three terms of which are l and the last three terms of which are T0；
S8: determining the zero point calibration and gravity compensation parameter F calculated in S6 and S70、T0、l、BG, if the precision requirement is met, repeating S2-S7 if the required precision requirement is not met, and completing the processes of zero point correction and gravity compensation parameter solving until the precision requirement is met, wherein the precision can be calculated by the following two formulas:
Figure BDA0002450544620000116
Figure BDA0002450544620000121
s9: and storing the obtained zero point correction and gravity compensation parameters on a hard disk.
After the process of zero point correction and gravity compensation parameter solving is completed, the zero point correction and gravity compensation can be performed on the measured value of the six-dimensional force sensor when the robot is in any pose, and fig. 3 shows a flow chart of the zero point correction and gravity compensation process. Referring to fig. 3, the zero point calibration and gravity compensation process of the present embodiment includes:
s1: loading zero correction and gravity compensation parameters from a hard disk;
s2: reading the current attitude of the tail end of the robot from the robot controllerGiving the quaternion form, converting the quaternion form into a rotation matrix form according to a conversion method of the step S3 in the process of solving zero point correction and gravity compensation parameters, and recording the rotation matrix form as a result
Figure BDA0002450544620000122
；
S3: reading a sensor reading in the current robot posture from a six-dimensional force sensor, and recording a force component and a moment component of the sensor reading as F and T;
s4: performing zero correction and gravity compensation on the sensor reading according to the zero correction and gravity compensation parameters obtained by solving, and performing zero correction and gravity compensation on the measured value of the six-dimensional force sensor acquired in real time according to the following formula
Figure BDA0002450544620000123
Figure BDA0002450544620000124
S5: and judging whether zero point correction and gravity compensation are needed, if so, repeating the steps from S2 to S4, and if not, exiting the zero point correction and gravity compensation process.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.

Claims (9)

1. A zero point correction and gravity compensation method for a six-dimensional force sensor is characterized by comprising the following steps:
step S1: zero point correction and gravity compensation parameter solution;
step S2: zero point correction and gravity compensation;
the zero point correction is performed simultaneously with the gravity compensation.
2. The zero-point calibration and gravity compensation method for a six-dimensional force sensor according to claim 1, wherein the zero-point calibration and gravity compensation parameters in step S1 include: zero drift value F of force component of six-dimensional force sensor0(ii) a Zero drift value T of moment component of six-dimensional force sensor0(ii) a Coordinates of gravity under robot base coordinate systemBG; and (3) the coordinate l of the center of gravity of the end effector under the sensor coordinate system.
3. The method for zero point calibration and gravity compensation of six-dimensional force sensor according to claim 1, wherein the zero point calibration and gravity compensation parameters in step S1 are calculated and obtained at a time after recording required data, the required data includes rotation transformation of the robot end relative to the robot base system and the six-dimensional force sensor reading when the robot is in different postures.
4. The zero point calibration and gravity compensation method for six-dimensional force sensor according to claim 1, wherein the step S1 further comprises the steps of:
step S11: moving the robot to a proper initial pose;
step S12: keeping the position of the tail end of the robot unchanged, randomly selecting the posture of the tail end of the robot, and moving the robot to the posture;
step S13: reading the current attitude of the tail end of the robot from the robot controller;
step S14: reading a sensor reading in the current robot posture from a six-dimensional force sensor;
step S15: judging whether the number of the currently recorded data groups is more than or equal to 3 groups, if so, repeating the step S12-the step S14, and otherwise, entering the next step;
step S16: calculating zero correction and gravity compensation parameters: coordinates of gravity under robot base coordinate systemBG and six-dimensional force sensor force componentZero drift value of F0；
Step S17: calculating zero correction and gravity compensation parameters: coordinate l of center of gravity of end effector under sensor standard coordinate system and zero drift value T of moment component of six-dimensional force sensor0；
Step S18: determining the zero point calibration and gravity compensation parameter F calculated in the steps S16 and S170、T0、l、BG, whether the precision requirement is met or not is judged, if the precision requirement is not met, the steps S12-S17 are repeated until the precision requirement is met;
step S19: and storing the obtained zero point correction and gravity compensation parameters on a storage medium.
5. The zero-point calibration and gravity compensation method for six-dimensional force sensor according to claim 4, wherein the sensor readings from the six-dimensional force sensor in step S14 include force component F and moment component T, each of which includes values in x, y and z directions.
6. The zero point calibration and gravity compensation method for six-dimensional force sensor according to claim 4, wherein the step S18 for determining whether the required accuracy is achieved is calculated by the following error formula:
Figure FDA0002450544610000021
Figure FDA0002450544610000022
wherein the content of the first and second substances,
Figure FDA0002450544610000023
for the robot pose recorded in step S13, Fi、TiForce component, moment component, F, respectively, of the six-dimensional force sensor reading recorded in step S140、T0、BG、lRespectively, zero correction and gravity compensation parameters: the zero drift value of the force component of the six-dimensional force sensor, the zero drift value of the moment component of the six-dimensional force sensor, the coordinate of the gravity under a robot base coordinate system and the coordinate of the gravity center of the end effector under a sensor coordinate system.
7. The zero point calibration and gravity compensation method for six-dimensional force sensor according to claim 1, wherein the step S2 further comprises the steps of:
step S21: loading the zero point correction and gravity compensation parameters saved in the step S1 from the storage medium;
step S22: reading the current attitude of the tail end of the robot from the robot controller;
step S23: reading a sensor reading in the current robot posture from a six-dimensional force sensor;
step S24: performing zero correction and gravity compensation on the sensor reading according to the zero correction and gravity compensation parameters obtained by the step S1;
step S25: and judging whether zero point correction and gravity compensation are needed, if so, repeating the step S22 to the step S25, and if not, exiting the zero point correction and gravity compensation process.
8. The zero-point calibration and gravity compensation method for six-dimensional force sensor according to claim 7, wherein in step S22, the sensor readings from the six-dimensional force sensor include a force component F and a moment component T, each of which includes values in x, y and z directions.
9. The zero-point calibration and gravity compensation method for six-dimensional force sensor according to claim 7, wherein the zero-point calibration and gravity compensation for the sensor reading in step S3 are calculated by the following equations:
Figure FDA0002450544610000024
Figure FDA0002450544610000025
wherein, Fr、TrRespectively the force and the moment born by the end effector after compensation, F, T respectively the force and the moment components of the measured value of the six-dimensional force sensor, F0、T0、BG. l is the zero drift value of the force component of the six-dimensional force sensor, the zero drift value of the moment component of the six-dimensional force sensor, the coordinate of the gravity under the robot base coordinate system and the coordinate of the gravity center of the end effector under the sensor coordinate system, which are obtained by the solution in the step S1.
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