CN112621746A - PID control method with dead zone and mechanical arm visual servo grabbing system - Google Patents

Abstract

The invention discloses a PID control method with a dead zone, which is used for controlling a mechanical arm visual servo grabbing system and comprises the following steps: calculating the deviation of the target pose of the object and the pose of the end effector; processing the deviation by using a dead zone module, then taking the deviation as the input of a PID controller, and taking the output of the PID controller as the Cartesian space velocity of an end effector; converting the Cartesian space velocity into a joint space velocity; and filtering the joint space velocity by using a second-order Butterworth filter, and then transmitting the joint space velocity to a mechanical arm velocity controller to realize the real-time control of the pose of the mechanical arm. The invention also provides a mechanical arm vision servo grabbing system using the method. The control method provided by the invention can solve the problem of 'shaking' caused by frequent adjustment of the mechanical arm control system when the end effector of the mechanical arm approaches the target pose, and is beneficial to realizing the stable control of the pose of the mechanical arm.

Description

PID control method with dead zone and robotic arm visual servo grasping system

technical field

The invention relates to the field of intelligent control, in particular to a PID control method with dead zone and a mechanical arm visual servo grabbing system using the method.

Background technique

With the rapid development of artificial intelligence, the improvement of the manufacturing level of robots and visual sensors, the combination of visual perception and robot technology has greatly improved the level of robot automation and intelligence. Among them, as a highly flexible robot, the robotic arm combined with visual perception technology has great application prospects in completing the intelligent grasping of objects, and can be widely used in automobile manufacturing, medical services, warehousing and logistics and other industries The research hotspot of foreign scholars. In order to achieve successful grasping of the target material, it is necessary to adjust the position and posture of the robot arm according to the position and posture of the target material fed back by the vision system. The closed-loop control of the robot arm is called visual servo control by combining visual perception with the control technology of the robot arm.

In the currently published visual servo control of a robotic arm, CN 110116410 A discloses a visual servo-based robotic arm target guidance system, which mainly solves the problems of occlusion and separation from the visual field of target imaging in visual servoing; CN108058171A discloses a A position-based and closed-loop control robotic arm visual servo system mainly involves the hardware implementation method of the system, but not the control algorithm; CN 110919654 A discloses the application of visual servoing in the field of robotic arm automatic docking, and the content does not involve the robotic arm Control algorithm; CN 107414825 A discloses a motion planning system for an industrial robot to smoothly grasp a moving object, mainly involving the content of path obstacle avoidance. The precise, stable and real-time control of the visual servo of the robotic arm is not involved in the above-mentioned prior art.

Accurately reaching the target material pose is the key to the successful grasping of the object by the robotic arm, so a reasonable controller needs to be designed to realize the closed-loop control of the robotic arm based on visual feedback. However, in the closed-loop control system, when the manipulator approaches the target pose, frequent adjustments will occur, which will cause the manipulator to “jitter” and cause damage to the manipulator drive system and hardware structure. In addition, in complex grasping scenarios such as warehousing and logistics industry materials are usually placed randomly and the pose may change, requiring the robotic arm to track the pose of the target material in real time. In summary, the realization of precise, stable and real-time control of the robotic arm is a problem that needs to be solved in the visual grasping of objects by the robotic arm.

Therefore, those skilled in the art are committed to developing a PID control method with dead zone and a robotic arm visual servo grasping system using the method. On the basis of realizing precise control of the position and posture of the robotic arm, the dead zone module can remove the The "jitter" problem when the end effector of the manipulator is close to the target pose is conducive to the stable control of the pose of the manipulator.

SUMMARY OF THE INVENTION

In order to achieve the above object, the present invention provides a PID control method with dead zone, the control method is used to control the visual servo grasping system of the robotic arm, and the control method includes:

Step 1: Calculate the deviation between the target pose of the object and the pose of the end effector of the robotic arm visual servo grasping system;

Step 2: use the dead zone module to process the deviation;

Step 3: take the deviation obtained in the step 2 as the input of the PID controller, and take the output of the PID controller as the Cartesian space velocity of the end effector;

Step 4: Convert the Cartesian space velocity obtained in the step 3 into joint space velocity;

Step 5: use the second-order Butterworth filter to filter the joint space velocity obtained in the step 4;

Step 6: Send the result obtained in Step 5 to the robot arm speed controller of the robot arm visual servo grasping system, so as to realize the real-time control of the pose of the robot arm.

In some embodiments, optionally, the control method further includes step 7: repeating the step 1 to the step 6.

In some embodiments, optionally, the relationship between the Cartesian space velocity of the end effector and the deviation obtained in the step 2 is as follows:

Wherein, V _e (t) represents the Cartesian space velocity, e(t) represents the deviation obtained in the step 2, and K _p , K _i and K _d are the proportional coefficient and integral of the PID controller, respectively. coefficients and differential coefficients.

In some embodiments, optionally, the step 3 includes:

Denote the Cartesian space velocity as V _e (t) = [v _x (t), v _y (t), v _z (t), w _x (t), w _y (t), w _z (t ),] ^T , where v _x (t), v _y (t) and v _z (t) represent the linear velocity of the end effector in the x, y and z-axis directions, respectively, ω _x (t), ω _y (t) and ω _z (t) represent the angular velocities of the end effector in the directions of the x, y and z axes, respectively;

The relationship between the deviation obtained in the step 2 and the v _x (t), v _y (t) and v _z (t) is as follows:

where e _x (t), e _y (t) and e _z (t) are the deviations between the position of the object and the position of the end effector in the x, y and z axis directions, respectively, where e _x (t)=x _g (t)-x _e (t), e _y (t)=y _g (t)-y _e (t), e _z (t)=z _g (t)-z _e (t ), x _g (t), y _g (t) and z _g (t) represent the position of the object in the x, y and z axis directions, respectively, x _e (t), y _e (t) and z _e (t) represents the position of the end effector in the x, y and z axis directions, respectively;

The angular velocity is expressed by a quaternion, and the relationship between the angular velocity and the quaternion is as follows:

Taking the result obtained by formula (3) through the step 2 as the differential expression of the quaternion as follows:

Among them, e _q0 (t), e _q1 (t), e _q2 (t) and e _q3 (t) are q _g0 (t), q _g1 (t), q _g2 (t) and q _g3 of the target pose, respectively Deviation between the (t) component and the q _e0 (t), q _e1 (t), q _e2 (t), and q _e3 (t) components of the actual pose.

In some embodiments, optionally, the step 4 includes the following steps:

Derive the forward kinematics model of the robotic arm based on the D-H method;

determining the linear velocity Jacobian matrix and the angular velocity Jacobian matrix of the end effector, and then obtaining the Jacobian matrix of the robotic arm;

The transformation from the Cartesian space velocity to the joint space velocity is obtained according to the Jacobian matrix of the robotic arm.

In some embodiments, optionally, the process of deriving the forward kinematics model of the robotic arm based on the D-H method is as follows:

According to the D-H method, the transformation matrix from coordinate system {i-1} to coordinate system {i} is obtained, and its homogeneous coordinate expression is:

Among them, c represents the cos function, and s represents the sin function;

The three ^- dimensional position and attitude of the end effector is expressed as _:

T ₀ ⁶ =T ₀ ¹ T ₁ ² T ₂ ³ T ₃ ⁴ T ₄ ⁵ T ₅ ⁶ (6)

The expression of the homogeneous coordinate transformation matrix T ₀ ⁶ of the end effector relative to the manipulator base coordinate system {0} is as follows:

为所述末端执行器姿态的旋转矩阵。where (p _x , p _y , p _z ) represents the position of the end effector in Cartesian space,

is the rotation matrix of the end effector pose.

In some embodiments, optionally, the calculation of the linear velocity Jacobian matrix is:

Differential derivation of the joint space vectors (θ ₁ , θ ₂ , θ ₃ , θ ₄ , θ ₅ , θ ₆ ) can obtain the expression of the linear velocity Jacobian matrix as follows:

Wherein, J _v represents the linear velocity Jacobian matrix;

The expression of each element in formula (8) is obtained according to formula (7).

In some embodiments, optionally, the expression of the angular velocity Jacobian matrix is as follows:

表示基坐标系到第i个关节坐标系的变换，

为所述变换矩阵T₀i中第三列前三行所对应的向量。where J _w represents the angular velocity Jacobian matrix,

Represents the transformation from the base coordinate system to the ith joint coordinate system,

is the vector corresponding to the first three rows of the third column in the transformation matrix T ₀ i.

The present invention also provides a visual servo control system for a robotic arm, comprising a main control computer, a robotic arm control cabinet, a six-joint robotic arm, an end effector and an RGBD camera;

The main control computer is connected with the RGBD camera; the robotic arm control cabinet is connected with the main control computer, the six-joint robotic arm is connected with the robotic arm control cabinet, and the end effector is arranged on the The end of the six-joint robotic arm, the end effector is connected to the control cabinet of the robotic arm;

Wherein, the RGBD camera is configured to be able to capture the image of the target object and transmit it to the main control computer; the main control computer is configured to be able to execute the control method as described above, and convert the execution result into the robotic arm joints space speed signal, and send the speed signal to the robotic arm control cabinet; the robotic arm control cabinet is configured to control the six-joint robotic arm according to the speed signal, so that the end effector reaches the target pose, and then control the end effector to grasp the object, and feed back the actual pose of the end effector to the main control computer.

In some embodiments, optionally, the end effector is a suction device.

The PID control method with dead zone provided by the present invention and the mechanical arm visual servo grasping system using the method have the following technical effects:

The robotic arm visual servo grasping system based on the dead zone PID controller of the present invention is mainly composed of a main control computer, a robotic arm control cabinet, a six-joint robotic arm, a suction cup device, an RGBD camera, etc., and can be applied to the storage and logistics industry materials. Sorting. Compared with the existing robotic arm control technology, the robotic arm visual servo grasping system with a dead zone PID controller proposed by the present invention realizes the precise control of the robotic arm pose and posture, and the dead zone module can remove the execution of the end of the robotic arm. When the robot approaches the target pose, the "jitter" problem caused by the frequent adjustment of the manipulator control system is beneficial to realize the stable control of the manipulator's pose. At the same time, in order to realize the real-time adjustment of the position and posture of the manipulator, the speed control mode of the manipulator is adopted, and the output value of the PID controller with dead zone is used as the speed of the end effector of the manipulator, which can realize the real-time tracking and grasping of the target material.

The concept, specific structure and technical effects of the present invention will be further described below in conjunction with the accompanying drawings, so as to fully understand the purpose, characteristics and effects of the present invention.

Description of drawings

Fig. 1 is the control block diagram of the PID control method with dead zone of the present invention;

FIG. 2 is a schematic diagram of the hardware composition of the robotic arm visual servo grabbing system of the present invention.

Detailed ways

The following describes several preferred embodiments of the present invention with reference to the accompanying drawings, so as to make its technical content clearer and easier to understand. The present invention can be embodied in many different forms of embodiments, and the protection scope of the present invention is not limited to the embodiments mentioned herein.

In the drawings, structurally identical components are denoted by the same numerals, and structurally or functionally similar components are denoted by like numerals throughout.

As shown in Figure 1, the PID control method with dead zone provided by the present invention comprises the following steps:

Step 1: Calculate the deviation e(t) between the target pose P _g of the object and the end effector pose P _e obtained by the forward kinematics model in step 5, and its expression is:

_e (t)= _Pg -Pe(1)

Step 2: In the present invention, in order to avoid the “jitter” of the robot arm caused by the frequent adjustment of the visual servo system of the robot arm when the end effector reaches the target pose, the deviation e(t) obtained in step 1 is added before inputting the PID controller. Dead zone module, its expression is:

In the dead zone module, the deviation e(t) is processed. If the deviation is outside the dead zone range, PID adjustment of the pose of the end effector is required; otherwise, the pose of the end effector does not need to be adjusted. Among them, e ₀ is the dead zone value, which needs to be determined according to the adjustment performance and control accuracy requirements of the PID controller with dead zone.

Step 3: Use the deviation e(t) obtained in Step 2 as the input of the PID controller, and use the output of the PID controller as the Cartesian space velocity _Ve (t) of the end effector. According to the expression of the PID controller, V _e (t) is obtained as formula (3), where K _p , K _i and K _d are the proportional coefficient, integral coefficient and differential coefficient of the PID controller, respectively.

The end effector of the robotic arm has six degrees of freedom, including three positions and three attitude angles, so the end effector velocity can be expressed as V _e (t)=[v _x (t),v _y (t),v _z (t),w _x (t),w _y (t),w _z (t),] ^T . The Cartesian space velocity of the end effector described in the present invention is based on the base coordinate system of the manipulator, and the linear velocity and the angular velocity will be analyzed separately below.

(1) Taking the calculation result of the PID controller with dead zone as the speed of the end effector of the manipulator, the linear speeds in the x, y and z axis directions are vx(t), vy(t) and vz(t) respectively, the expression for:

where e _x (t), e _y (t) and e _z (t) are the deviations between the target position and the position of the end effector of the manipulator in the x, y and z axis directions, that is, e _x (t)=x _g (t) _-xe (t), _ey (t)= _yg (t) _-ye (t), _ez (t)= _zg (t) _-ze (t).

角速度与四元数的微分存在以下关系：(2) There are various expressions for the pose of the end effector of the manipulator, including rotation matrix, rotation vector, Euler angle and quaternion. Among them, the quaternion is not only compact, but also has no singularity, so the present invention analyzes the angular velocity of the end effector based on the quaternion. The quaternion expression is

The angular velocity is related to the differential of the quaternion as follows:

The result obtained by the quaternion deviation through the PID algorithm with dead zone is used as the differential expression of the quaternion, namely:

Among them, e _q0 (t), e _q1 (t), e _q2 (t) and e _q3 (t) are q _g0 (t), q _g1 (t), q _g2 (t) and q _g3 of the target pose, respectively Deviation between the (t) component and the q _e0 (t), q _e1 (t), q _e2 (t), and q _e3 (t) components of the actual pose.

Step 4: The Cartesian space velocity of the manipulator cannot be directly sent to the manipulator speed controller. It needs to be converted into the joint space velocity, which involves the instantaneous kinematics model of the manipulator. The derivation process is as follows:

(1) The forward kinematics model of the manipulator is derived based on the D-H method, and the instantaneous kinematics model is derived on this basis to realize the conversion from Cartesian space velocity to joint space velocity. For the convenience of expression, the cos function and sin function are simplified to c and s respectively. According to the D-H parameter method, the transformation matrix from coordinate system {i-1} to coordinate system {i} can be obtained. The homogeneous coordinate expression is:

The three-dimensional position and attitude of the end effector can be understood as a transformation matrix relative to the base coordinate system {0} of the manipulator, namely T ₀ ⁶ . According to the relationship between adjacent coordinate systems, the conversion from the end effector to the base coordinate system can be obtained as:

T ₀ ⁶ =T ₀ ¹ T ₁ ² T ₂ ³ T ₃ ⁴ T ₄ ⁵ T ₅ ⁶ (8)

On the premise of determining the joint position θ _i , the pose of the end effector in the base coordinate system {0} of the manipulator can be determined. The homogeneous coordinate transformation matrix of the end effector of the manipulator relative to the base coordinate system {0} has an expression in the form of formula (9):

为末端执行器姿态的旋转矩阵。根据公式(7)和公式(8)以及在确定各关节转角的条件下即可确定公式(9)中各元素的表达式。where (p _x , p _y , p _z ) represents the position of the end effector in Cartesian space,

is the rotation matrix for the pose of the end effector. The expression of each element in formula (9) can be determined according to formula (7) and formula (8) and under the condition of determining the rotation angle of each joint.

的映射关系，表达式为：(2) In the design of the visual servo controller, the calculation result of the PID algorithm with dead zone is used as the speed of the end effector. In order to realize the control of the manipulator, it is necessary to convert the Cartesian space velocity to the joint space velocity. The Jacobian matrix J establishes the joint space velocity q to the Cartesian space velocity

The mapping relationship of , the expression is:

因此首先需要确定雅可比矩阵J的表达式。为便于推导，将机械臂雅可比矩阵拆分为两部分，即J＝[J_v,J_w]^T，其中J_v和J_w分别表示末端执行器线速度和角速度雅可比矩阵。首先对J_v进行推导，在机械臂正运动学模型中(p_x,p_y,p_z)表示末端执行器位置，对关节空间向量(θ₁,θ₂,θ₃,θ₄,θ₅,θ₆)进行微分求导可以得到J_v的表达式如公式(11)所示，根据公式(9)可以得到公式(11)中各元素的表达式。Through the pseudo-inverse transformation of the Jacobian matrix J, the expression of the joint space velocity can be obtained as

Therefore, the expression of the Jacobian matrix J needs to be determined first. For the convenience of derivation, the manipulator Jacobian matrix is divided into two parts, namely J=[J _v , J _w ] ^T , where J _v and J _w represent the end effector linear velocity and angular velocity Jacobian matrix, respectively. Firstly, J _v is deduced. In the forward kinematics model of the manipulator (p _x , p _y , p _z ) represents the position of the end effector, and the joint space vectors (θ ₁ , θ ₂ , θ ₃ , θ ₄ , θ ₅ ) represent the position of the end effector. , θ ₆ ) can be differentiated to obtain the expression of J _v as shown in formula (11), and the expression of each element in formula (11) can be obtained according to formula (9).

How many degrees the manipulator's rotary joint rotates around its own axis of rotation will correspondingly cause the end effector to rotate around this axis. The angular velocity in the three-dimensional space is a vector pointing to the rotation axis. Each rotating joint of the manipulator rotates around its own Z axis. If the joint rotation speed under a certain rotation axis is w, the unit angular velocity vector of the end effector based on the rotation axis is [0,0,1]. In order to obtain the angular velocity part J _w of the Jacobian matrix, it is necessary to transform the reference system of each rotary joint into the base coordinate system, and the expression of the angular velocity part J of the Jacobian matrix can be obtained as:

表示基坐标系到第i个关节坐标系的变换，根据机械臂正运动学模型推导过程，可知

为变换矩阵T₀ ⁱ中第三列前三行所对应的向量，因而得到J_w中各项的表达式。in,

Represents the transformation from the base coordinate system to the ith joint coordinate system. According to the derivation process of the forward kinematics model of the manipulator, it can be seen that

is the vector corresponding to the first three rows of the third column in the transformation matrix T ₀ ⁱ , and thus the expressions of the terms in J _w are obtained.

即可得到笛卡尔空间速度到关节空间速度的变换。Combining formula (11) and formula (12), the manipulator Jacobian matrix J can be obtained, according to the formula

The transformation from Cartesian space velocity to joint space velocity can be obtained.

Step 5: Due to the existence of interference information, the joint space velocity obtained in step 4 will fluctuate. In order to achieve smooth and stable control of the manipulator, a second-order Butterworth filter with good comprehensive performance is used for the joint obtained in step 4. The spatial velocity is filtered.

Step 6: Send the joint space velocity obtained in Step 5 to the speed controller of the manipulator to realize real-time control of the pose of the manipulator.

Step 7: Repeat steps 1-6 to achieve accurate, stable and real-time adjustment of the pose of the end effector of the robotic arm relative to the target pose.

Based on the above-mentioned PID control method with dead zone, the present invention proposes a mechanical arm visual servo grasping system, as shown in FIG. 2 . The mechanical arm visual servo grabbing system based on the dead zone PID controller proposed by the present invention mainly includes a main control computer, a mechanical arm control cabinet, a six-joint mechanical arm, an end effector, and an RGBD camera. The main control computer is connected to the RGBD camera; the robotic arm control cabinet is connected to the main control computer, the six-joint robotic arm is connected to the robotic arm control cabinet, and the end effector is set at the end of the six-joint robotic arm to grasp the target material. The end effector is also connected with the robotic arm control cabinet. The RGBD camera collects the two-dimensional image and depth image of the target material, and transmits it to the main control computer in real time; the main control computer performs the target material recognition and pose calculation, and converts the pose result to the base coordinate system of the robot arm as a reference. The target pose; the main control computer performs the calculation of the PID control method with dead zone, and converts the calculation result into the speed signal of the joint space of the manipulator. The speed control signal is sent to the manipulator control cabinet for real-time control of the six-joint manipulator. At the same time, when the manipulator end effector reaches the target pose, the manipulator control cabinet outputs a grasping signal to the suction cup device. The actual pose of the joint manipulator is fed back to the main control computer to realize the closed-loop control of the pose of the manipulator. In some embodiments, the end effector may choose a suction cup arrangement.

Compared with the existing robotic arm control technology, the robotic arm visual servo grasping system with a dead zone PID controller proposed by the present invention realizes the precise control of the robotic arm pose and posture, and the dead zone module can remove the execution of the end of the robotic arm. When the robot approaches the target pose, the "jitter" problem caused by the frequent adjustment of the manipulator control system is beneficial to realize the stable control of the manipulator's pose. At the same time, in order to realize the real-time adjustment of the position and posture of the manipulator, the speed control mode of the manipulator is adopted, and the output value of the PID controller with dead zone is used as the speed of the end effector of the manipulator, which can realize the real-time tracking and grasping of the target material.

The preferred embodiments of the present invention have been described in detail above. It should be understood that many modifications and changes can be made according to the concept of the present invention by those skilled in the art without creative efforts. Therefore, all technical solutions that can be obtained by those skilled in the art through logical analysis, reasoning or limited experiments on the basis of the prior art according to the concept of the present invention shall fall within the protection scope determined by the claims.

Claims (10)

1. a PID control method with dead zone, is characterized in that, described control method is used to control mechanical arm visual servo grasping system, and described control method comprises: Step 1: Calculate the deviation between the target pose of the object and the pose of the end effector of the robotic arm visual servo grasping system; Step 2: use the dead zone module to process the deviation; Step 3: take the deviation obtained in the step 2 as the input of the PID controller, and take the output of the PID controller as the Cartesian space velocity of the end effector; Step 4: Convert the Cartesian space velocity obtained in the step 3 into joint space velocity; Step 5: use the second-order Butterworth filter to filter the joint space velocity obtained in the step 4; Step 6: Send the result obtained in Step 5 to the robot arm speed controller of the robot arm visual servo grasping system, so as to realize the real-time control of the pose of the robot arm. 2 . The PID control method with dead zone according to claim 1 , wherein the control method further comprises step 7 : repeating the step 1 to the step 6 . 3 . 3. The PID control method with dead zone as claimed in claim 1, wherein the relationship between the Cartesian space velocity of the end effector and the deviation obtained in the step 2 is as follows:

Wherein, V _e (t) represents the Cartesian space velocity, e(t) represents the deviation obtained in the step 2, and K _p , K _i and K _d are the proportional coefficient and integral of the PID controller, respectively. coefficients and differential coefficients. 4. the PID control method with dead zone as claimed in claim 3, is characterized in that, described step 3 comprises: Denote the Cartesian space velocity as V _e (t) = [v _x (t), v _y (t), v _z (t), w _x (t), w _y (t), w _z (t ),] ^T , where v _x (t), v _y (t) and v _z (t) represent the linear velocity of the end effector in the x, y and z-axis directions, respectively, ω _x (t), ω _y (t) and ω _z (t) represent the angular velocities of the end effector in the directions of the x, y and z axes, respectively; The relationship between the deviation obtained in the step 2 and the v _x (t), v _y (t) and v _z (t) is as follows:

where e _x (t), e _y (t) and e _z (t) are the deviations between the position of the object and the position of the end effector in the x, y and z axis directions, respectively, where e _x (t)=x _g (t)-x _e (t), e _y (t)=y _g (t)-y _e (t), e _z (t)=z _g (t)-z _e (t ), x _g (t), y _g (t) and z _g (t) represent the position of the object in the x, y and z axis directions, respectively, x _e (t), y _e (t) and z _e (t) represents the position of the end effector in the x, y and z axis directions, respectively; The angular velocity is expressed by a quaternion, and the relationship between the angular velocity and the quaternion is as follows:

Taking the result obtained by formula (3) through the step 2 as the differential expression of the quaternion as follows:

Among them, e _q0 (t), e _q1 (t), e _q2 (t) and e _q3 (t) are q _g0 (t), q _g1 (t), q _g2 (t) and q _g3 of the target pose, respectively Deviation between the (t) component and the q _e0 (t), q _e1 (t), q _e2 (t), and q _e3 (t) components of the actual pose. 5. the PID control method with dead zone as claimed in claim 4, is characterized in that, described step 4 comprises the steps: Derive the forward kinematics model of the robotic arm based on the D-H method; determining the linear velocity Jacobian matrix and the angular velocity Jacobian matrix of the end effector, and then obtaining the Jacobian matrix of the robotic arm; The transformation from the Cartesian space velocity to the joint space velocity is obtained according to the Jacobian matrix of the robotic arm. 6. The PID control method with dead zone as claimed in claim 5, wherein the process of deriving the forward kinematics model of the robotic arm based on the D-H method is as follows: According to the D-H method, the transformation matrix from coordinate system {i-1} to coordinate system {i} is obtained, and its homogeneous coordinate expression is:

Among them, c represents the cos function, and s represents the sin function; The three ^- dimensional position and attitude of the end effector is expressed as _:

The expression of the homogeneous coordinate transformation matrix T ₀ ⁶ of the end effector relative to the manipulator base coordinate system {0} is as follows:

where (p _x , p _y , p _z ) represents the position of the end effector in Cartesian space,

is the rotation matrix of the end effector pose. 7. The PID control method with dead zone as claimed in claim 6, wherein the calculation of the linear velocity Jacobian matrix is: for joint space vectors (θ ₁ , θ ₂ , θ ₃ , θ ₄ , θ ₅ , θ ₆ ) to perform differential derivation to obtain the expression of the linear velocity Jacobian matrix, as follows:

Wherein, J _v represents the linear velocity Jacobian matrix; The expression of each element in formula (8) is obtained according to formula (7). 8. the PID control method with dead zone as claimed in claim 6, is characterized in that, the expression of described angular velocity Jacobian matrix is as follows:

where J _w represents the angular velocity Jacobian matrix,

Represents the transformation from the base coordinate system to the ith joint coordinate system,

for the transformation matrix

The vector corresponding to the first three rows of the third column in . 9. A visual servo control system for a robotic arm, comprising a main control computer, a robotic arm control cabinet, a six-joint robotic arm, an end effector and an RGBD camera; The main control computer is connected with the RGBD camera; the robotic arm control cabinet is connected with the main control computer, the six-joint robotic arm is connected with the robotic arm control cabinet, and the end effector is arranged on the The end of the six-joint robotic arm, the end effector is connected to the control cabinet of the robotic arm; Wherein, the RGBD camera is configured to be able to capture the image of the target object and transmit it to the main control computer; the main control computer is configured to be able to execute the control method according to any one of claims 1-8, and Converting the execution result into a speed signal in the joint space of the manipulator, and sending the speed signal to the manipulator control cabinet; the manipulator control cabinet is configured to control the six-joint manipulator according to the speed signal, The end effector is made to reach the target pose, and then the end effector is controlled to grab the object, and the actual pose of the end effector is fed back to the main control computer. 10 . The visual servo control system for a robotic arm according to claim 9 , wherein the end effector is a suction device. 11 .

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