CN110614636A - Measurement time lag compensation method for visual servo robot - Google Patents
Measurement time lag compensation method for visual servo robot Download PDFInfo
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- CN110614636A CN110614636A CN201910986420.4A CN201910986420A CN110614636A CN 110614636 A CN110614636 A CN 110614636A CN 201910986420 A CN201910986420 A CN 201910986420A CN 110614636 A CN110614636 A CN 110614636A
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Classifications
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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
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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
- B25J9/1653—Programme controls characterised by the control loop parameters identification, estimation, stiffness, accuracy, error analysis
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- Feedback Control In General (AREA)
Abstract
The invention discloses a measurement time lag compensation method for a vision servo robot. The method compensates the measurement time lag of the visual servo robot, and estimates the interference and the difference in the system by using an estimator. And predicting the current time state and interference by combining with the measurement output, and designing a composite controller by utilizing feedback linearization. And the composite controller feeds the predicted value back to the visual servo robot to guide the robot to work. The invention increases the stability of the system, increases the feedback gain of the system, and improves the dynamic response speed, thereby obviously improving the servo control performance of the robot.
Description
Technical Field
The invention relates to a measurement time lag compensation method of a visual servo robot, and belongs to the technical field of high-performance control of visual servo robots.
Background
The visual servo robot is an important component in the robot field, and has wide application in the fields of automatic production, modern logistics, national defense and police affairs, aerospace and the like. The vision servo robot control can be classified into a position-based and an image-based vision servo control according to the use of the image signal. The position-based visual servo control needs three-dimensional reconstruction, depends on the calibration precision of a camera, and needs to be calibrated again after the environment is changed. The visual servo control based on the image directly defines the error on the image plane, avoids the calibration problem and has better robustness to environmental change and camera parameter perturbation.
The visual servo robot system is a multivariable nonlinear system and has the characteristics of variable interference, strong coupling and large measurement time lag. The measurement time lag is the time consumed by the image information in the processes of acquisition, transmission and processing, and the time is relatively large relative to the robot servo. The measurement skew may not only degrade the control performance of the servo system, but may even destroy the stability of the servo system. The traditional control method does not consider measurement time lag during design, so in order to ensure the stability of the system, only slow dynamic response can be selected when the parameters of the controller are adjusted, and a high-performance servo control effect is difficult to obtain. Classical interference estimator-based methods are also subject to measurement time lag when compensating for disturbances in the visual servoing system, thereby reducing the effectiveness of the disturbance compensation. When the visual servo robot tracks an unknown track, the measurement time lag can seriously affect the accuracy of the existing prediction method, so that the tracking precision is not high and the tracking speed is not high.
Aiming at the measurement time lag existing in a visual servo robot, a Smith predictor is usually adopted in the existing visual measurement time lag compensation, but the method has high requirement on the precision of a model established by the system and is difficult to realize in practical application. Other compensation methods do not consider the interference condition in the system, and the interference condition is not accordant with the actual condition of the visual servo robot system, so that the control performance of the system is reduced.
Disclosure of Invention
In order to solve the existing problems, the invention discloses an uncertainty compensation method for an industrial robot, which designs a composite controller by constructing a lumped uncertainty estimator and combining the lumped uncertainty estimator with a feedback linearization algorithm. The method simplifies the design process of the industrial robot controller, reduces the design cost, effectively compensates the lumped uncertainty and realizes the high-precision position control of the industrial robot. The specific technical scheme is as follows:
step 1, mounting encoders on joints of a multi-axis industrial robot, acquiring angle information and angular speed information of the joints, and transmitting the angle information and the angular speed information to an industrial robot controller in real time;
step 2, selecting the angle of each joint as a state variable of an industrial robot kinetic equation, and establishing a state space model of the multi-axis industrial robotWhereinis a state vector, representing the angle of each joint,is a state vectorThe first time derivative of (a), representing the angular velocity of each joint,is a state vectorThe second time derivative of (a), representing the angular acceleration of each joint;
step 3, introducing auxiliary vectorsWherein,Then, the multi-axis industrial robot state space model in the step 2 is transformed into a serial type state space modelWhereinRepresenting a lumped uncertainty vector;
step 4, constructing a lumped uncertainty estimator according to the serial industrial robot state space model obtained in the step 3Obtaining lumped uncertainty vectorsIs estimated value of；
Step 5, estimating the lumped uncertainty according to the step 4Combining the angles of the joints in step 1And angular velocityInformation, giving composite controller based on feedback linearization algorithmWhereinRepresenting the controller parameters to be designed.
In the state space model of the multi-axis industrial robot in the step 2A vector representing the input of the moment is shown,representing uncertainty vectors resulting from parameter uncertainties, friction moments and environmental disturbances,is a matrix of the moments of inertia,is a centripetal force coupling matrix that is,is a gravity matrix.
In the lumped uncertainty estimator in said step 4Representing a vectorIs determined by the estimated value of (c),representing a vectorIs determined by the estimated value of (c),representing the estimator parameters to be designed for,representing a symbolic function.
The estimator parameter to be designed in the lumped uncertainty estimator in the step 4Respectively as follows:
satisfies the conditionsAndwhereinRespectively representing the first time derivative of the lumped uncertainty vectorThe upper bound of the three components.
The controller parameters to be designed in the composite controller in the step 5The concrete expression is as follows:
whereinSatisfies the conditionsFor adjusting the rate of convergence of the state vector.
The invention has the beneficial effects that:
1. according to the invention, through compensation of measurement time lag in the vision servo robot, the stability margin of the system is increased, the feedback gain of the system is increased, and the dynamic response speed is improved, so that the servo control performance of the robot is obviously improved.
2. The invention can estimate the interference more accurately by the interference estimator for measuring time lag, thereby directly offsetting the interference in the system and improving the robustness and the control precision of the visual servo robot system.
Drawings
FIG. 1 is a schematic diagram of the steps of the present invention for compensating the measurement time lag of the vision servo robot.
FIG. 2 is a schematic structural diagram of a two-axis vision servo robot according to the present invention.
FIG. 3 is a control flow chart of the method for compensating the measurement time lag of the vision servo robot according to the present invention.
Detailed Description
The invention is further elucidated with reference to the drawings and the detailed description. It should be understood that the following detailed description is illustrative of the invention only and is not intended to limit the scope of the invention.
The invention provides a method for compensating measurement time lag of a visual servo robot by combining with figures 1-3, which comprises the following steps:
step 1: as shown in fig. 2, a camera is installed on an inner shaft of the two-shaft vision servo robot, the camera shoots a moving target in real time, a characteristic value of the moving target is extracted according to an image shot by the camera, and a controller of the two-shaft vision servo robot generates angular velocities of two shafts of the robot according to the characteristic value. The inner shaft and the outer shaft of the robot are provided with encoders to acquire angular velocity information, the two-shaft vision servo robot comprises the outer shaft and the inner shaft, and the camera is arranged on the inner shaft. And extracting a characteristic value of the moving target according to the acquired picture information. The controller calculates the desired angular velocity on each axis based on the characteristic values.
Step 2: selecting a characteristic value of a moving target as a system state, taking angular velocities at two axes as control input, setting a measurement time lag of the visual servo robot to be 2 sampling periods, and establishing a system discrete time state space model considering the measurement time lag and interference:
wherein,the status of the system is indicated,the control input of the control system is shown,representing the kinematic uncertainty of the system,which represents the measured output of the system and,a matrix of control inputs is represented that,represents the firstThe time of day.
In a model、、Andrespectively expressed as:
wherein,andrespectively representing the components of the moving object feature values in the horizontal and vertical directions of the image plane,andrepresenting the angular velocity of the camera on the outer and inner axes respectively,andrespectively representing the disturbances of the visual servorobot on the outer and inner axes,andrepresenting the measured values of the characteristic values of the moving object in the horizontal and vertical directions of the image plane, respectively, and controlling the input matrixAnd interferenceRespectively as follows:
and step 3: definition ofConstructing an improved expansion state estimator for the difference of the system interference according to the discrete time state space model established in the step 2:
wherein,、andrepresenting the states of the estimator, respectively、Andis determined by the estimated value of (c),、andthe estimator parameters are represented and specifically selected as follows:
and 4, step 4: according to the estimated value in step 3、、And step 2, calculating the predicted value of the current state of the system by using the discrete time state space modelAnd interference predictionThe specific calculation process is as follows:
step 5, obtaining the predicted value according to the step 4Anddesigning a composite controller based on feedback linearizationWhereinThe method specifically comprises the following steps:
the technical means disclosed by the scheme of the invention are not limited to the technical means disclosed by the technical means, and the technical scheme also comprises the technical scheme formed by any combination of the technical characteristics.
In light of the foregoing description of the preferred embodiment of the present invention, many modifications and variations will be apparent to those skilled in the art without departing from the spirit and scope of the invention. The technical scope of the present invention is not limited to the content of the specification, and must be determined according to the scope of the claims.
Claims (4)
1. A method for compensating measurement time lag of a visual servo robot is characterized by comprising the following steps:
the method considers the interference in the system when compensating the measurement time lag, utilizes the estimator to estimate the interference and the difference thereof in the system, combines the measurement output to predict the state and the interference at the current moment, and utilizes the feedback linearization to design the composite controller, and the method mainly comprises the following steps:
step 1: the method comprises the steps that encoders are arranged on all shafts of a visual servo robot, angular velocity information of all the shafts is obtained and is transmitted to a robot controller in real time, and a camera is arranged on the innermost shaft of the robot to obtain an image characteristic value of an environment object;
step 2: selecting an image characteristic value in a camera as a state variable of a system, taking the angular velocity of each joint of the robot as an input variable, and establishing a discrete time state space model considering measurement time lag and interference:
wherein,indicating the status of the visual servo robot system,a control input of the system is represented,which is indicative of the interference in the system,which represents the output of the measurement and is,which represents the time lag of the measurement,a matrix of control inputs is represented that,represents the firstTime of day;
and step 3: definition ofFor the difference of the system interference, according to the discrete time state space model established in the step 2, an improved expansion state estimator is constructed as follows:
wherein,、andrepresenting the states of the estimator, respectively、Andis determined by the estimated value of (c),、andrepresenting an estimator parameter;
and 4, step 4: according to the estimated value in step 3、、And step 2, calculating the predicted value of the current state of the system by using the discrete time state space modelAnd interference prediction；
And 5: according to the predicted value obtained in the step 4Anddesigning a composite controller based on feedback linearization，Representing a controller parameter.
2. The method of claim 1, wherein the estimator parameters of the improved dilation state estimator of step 3 are used to compensate for the visual servo robot measurement time lag、Andthe conditions are satisfied: square matrixIs within the unit circle.
3. The method as claimed in claim 1, wherein the predicted value of the disturbance at the current time in step 4 is used as the prediction value of the disturbance at the current timeAnd the predicted value of the stateThe specific calculation process is as follows:
。
4. the method as claimed in claim 1, wherein the controller parameters in the composite controller in step 5 are used to compensate the measurement time lag of the vision servo robotThe conditions are satisfied:is a diagonal matrix and the absolute value of the elements on the diagonal is less than 1.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114095872A (en) * | 2021-11-24 | 2022-02-25 | 南京工程学院 | Quick positioning system and method based on machine vision feedback |
| CN114347031A (en) * | 2022-01-18 | 2022-04-15 | 广东省智能机器人研究院 | Mobile mechanical arm collision avoidance control method and device considering time-varying time lag |
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2019
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114095872A (en) * | 2021-11-24 | 2022-02-25 | 南京工程学院 | Quick positioning system and method based on machine vision feedback |
| CN114347031A (en) * | 2022-01-18 | 2022-04-15 | 广东省智能机器人研究院 | Mobile mechanical arm collision avoidance control method and device considering time-varying time lag |
| CN114347031B (en) * | 2022-01-18 | 2024-01-16 | 广东省智能机器人研究院 | Mobile mechanical arm collision prevention control method and device considering time-varying time delay |
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Application publication date: 20191227 |