CN118438312A - A remote operation method for a polishing robot - Google Patents

Abstract

The invention discloses a teleoperation method of a polishing robot, which comprises the steps of determining the position of a polishing target point on the surface of an object to be polished in a virtual space when the position is guided, calculating the distance between the tail end point of a mechanical arm and the polishing target point, and if the distance is larger than a distance threshold value, adopting a cylindrical channel to conduct virtual force guidance with preferential distance, otherwise adopting a funnel-shaped channel to conduct virtual force guidance with preferential precision; when the gesture is guided, determining a normal line at a polishing target point, converting an Euler angle of the normal line gesture from a virtual space coordinate system to a robot coordinate system, subtracting the current gesture of the mechanical arm from the normal line gesture, and calculating a gesture difference value between the two; and generating a virtual force guide close to the target gesture according to the difference value. The invention can realize a more accurate auxiliary teleoperation process and obviously improve the operation precision and efficiency.

Description

A remote operation method for a polishing robot

Technical Field

The invention relates to robot motion control, and in particular to a remote operation method for a polishing robot.

Background technique

The traditional control method of the polishing robot adopts pre-programming or handle control. For the object to be polished, when the polishing operation is carried out, due to the uncertainty of the shape and position of the object generated in the previous processing process, it cannot be completed through the traditional teaching function of the robot, and the participation of the operator is required. Labor costs are constantly increasing, and the large amount of dust in the polishing environment will endanger the health of the operator. The robot is remotely controlled by a teleoperation device, and the operator can safely participate in the robot polishing operation. CN114643576A discloses a human-machine collaborative target grasping method based on virtual force guidance, which uses a virtual force field for obstacle avoidance and constructs a force field to generate guidance for approaching tasks, but its guidance method is less efficient, and the guidance content only includes position guidance, and the robot arm posture guidance is not realized.

Summary of the invention

Purpose of the invention: The purpose of the present invention is to provide a remote operation method for a grinding robot with high position guidance efficiency.

Technical solution: The remote operation method of the polishing robot described in the present invention, the polishing robot is a mechanical arm with a six-dimensional force sensor at the end, and the force feedback is achieved through force feedback master control; the remote operation method includes:

(1) Establish a virtual space including the polishing robot, the object to be polished, and the surrounding environment. The virtual space realizes visual feedback through VR glasses; performs gravity compensation on the six-dimensional force sensor, performs coordinate transformation and workspace matching on the force feedback master hand and the robotic arm, and realizes the movement operation of the force feedback master hand on the robotic arm;

(2) determining the position of the grinding target point on the surface of the object to be ground in the virtual space;

(3) Calculate the distance between the end point of the robot arm and the grinding target point. If the distance is greater than the distance threshold, execute step (4); otherwise, execute step (5);

(4) Construct a virtual force guide with distance priority in the cylindrical channel. When the end point of the robot arm is within the cylindrical guide channel, no force feedback is performed. When the end point of the robot arm exceeds the cylindrical guide channel, a virtual force guide is generated in the direction of the point in the cylindrical guide channel closest to the end point of the robot arm. Then return to step (3).

(5) constructing a virtual force guide with a priority on the accuracy of the funnel-shaped channel generation. If the end point of the robot arm is in the funnel-shaped channel, generate a virtual force guide toward the central axis and the polishing target point according to the position of the end point of the robot arm, wherein the central axis is the line connecting the end point of the robot arm and the polishing target point; then return to step (3);

(6) Repeat steps (3) to (5) until the grinding target point is reached.

Furthermore, in step (1), performing gravity compensation on the six-dimensional force sensor includes:

Measure the values of the six-dimensional force sensor in different postures, and calculate the tool gravity and the position of the center of mass of the six-dimensional force sensor:

Wherein, G is the tool gravity; L _x , _Ly , L _z are the coordinate positions of the center of mass in the sensor coordinate system, F is the measured axial force, and T is the measured torque.

Furthermore, step (2) includes: establishing a plane coordinate system with three known corner points O, A and B on the bottom surface of the object to be polished, with the OA direction as the X-axis and the OB direction as the Y-axis; then establishing a space coordinate system with the direction perpendicular to OAB and toward the polishing target point P as the Z-axis; translating point P along the negative direction of the Y-axis to the boundary line, set as point P′, and the line connecting PP′ is the coordinate of the Y-axis; drawing a line from point P′ to OA along the negative direction of the Z-axis, which is the coordinate of point P on the Z-axis in the coordinate system; the distance between point O and the line is the coordinate of the X-axis; thereby obtaining the coordinate position of point P relative to point O (Px, Py, Pz).

Furthermore, in step (3), the distance threshold is 10% of the length of the robotic arm.

Further, in step (4), a cylindrical guide channel is generated in the virtual space based on the coordinates of the end point of the robot arm as the starting point and the coordinates of the grinding target point as the end point;

The calculation formula of the virtual force _Fd of the cylindrical guide channel is:

F _d = k _d δ(X _d )

δ(X _d )＝X _d −D(X _d )

Wherein, _Fd is the guiding force vector, _kd is the feedback coefficient of force feedback; δ( _Xd ) is a vector, the direction of which is from the end point of the robot arm to the axis of the cylindrical guiding channel, and the magnitude is the distance from the end point of the robot arm to the axis of the cylindrical guiding channel; _rd is the radius of the cylindrical guiding channel; _Xd represents the coordinate of the end point of the robot arm in the virtual space, D( _Xd ) represents the point on the guiding path that is closest to the end point of the robot arm; a is a value greater than 0.

Further, in step (5), the funnel-shaped guide channel is generated with the line between the end point of the robot arm and the grinding target point as the central axis and the distance as the height, wherein the grinding target point is the top surface and the end point of the robot arm is the bottom surface;

The calculation formula of the virtual force _Ff of the funnel-shaped guide channel is:

F _f ＝F _sin +F _cos ＝k _sin δ _sin (X _f )+k _cos δ _cos (X _f )

F _sin is the force of the sine component of the force feedback at the end of the robotic arm within the funnel range, F _cos is the force of the cosine component of the force feedback at the end of the robotic arm within the funnel range, k _sin is the feedback coefficient of the sine component of the force feedback at the end of the robotic arm within the funnel range, k _cos is the feedback coefficient of the cosine component of the force feedback at the end of the robotic arm within the funnel range; δ _sin (X _f ) is the vector pointing to the axis of the funnel from the end point of the robotic arm; δ _cos (X _f ) is the vector parallel to the axis of the funnel from the end point of the robotic arm; X _f is the position of the end point of the robotic arm.

Furthermore, in step (5), the method for determining whether the end point of the robot arm is within the funnel-shaped channel is:

Obtain the vector δ _sin (X _f ) from the end point of the robot arm to the funnel axis and the vector δ (X _f ) from the end point of the robot arm to the polishing target point;

The sine value of the angle between the line connecting the current point of the robot arm and the grinding target point and the central axis of the funnel is calculated by |δ _sin (X _f )|/δ(X _f ). If the calculated sine value is less than sinα and |δ _sin (X _f )|<r _f , it is judged that the end point X _f of the robot arm is within the range of the funnel; α is the funnel opening angle, and r _f is the radius of the bottom of the funnel.

Furthermore, the polishing robot remote operation method also includes:

(7) Determine the normal line at the polishing target point;

(8) Perform coordinate system conversion on the Euler angles of the normal posture, first convert the virtual space coordinate system into the transition coordinate system, and then convert the transition coordinate system into the robot coordinate system; use quaternion operation to avoid the universal lock problem of Euler angles, first calculate the quaternion required to convert the Euler angles of the virtual space coordinate system into the transition coordinate system, then calculate the quaternion of the transition coordinate system rotated into the robot coordinate system, multiply the two quaternions, and obtain the rotation transformation required to convert the Euler angles in the virtual space into the Euler angles in the robot coordinate system;

(9) Virtual force feedback guides the posture, obtains the current posture of the robot arm, subtracts the normal posture from the robot arm posture, and calculates the difference between the two postures; based on the difference, generates a virtual force guidance close to the target posture.

Furthermore, step (7) includes: selecting the vertex on the model of the object to be polished in the virtual space that is closest to the polishing target point as the basic vertex a, and obtaining the other two points b and c that form a triangle with the basic vertex a; subtracting the coordinates of the basic vertex a from the coordinates of points b and c respectively to obtain two vectors Side1 and Side2; performing a cross product on the two vectors to obtain a third vector η that is perpendicular to the two vectors, and the direction of the third vector η is the normal direction at the polishing target point.

Furthermore, step (8) includes: calculating the quaternion q _mid required to transform the Euler angle of the virtual space coordinate system into the transition coordinate system:

q _mid = qz*qy*qx

Among them, (eulerx, eulery, eulerz) is the Euler angle in the virtual space coordinate system;

Calculate the quaternion q _sec of the transition coordinate system rotation to the robot coordinate system:

The rotation transformation required from the virtual space coordinate system to the robot coordinate system is: q _end =q _mid *q _sec .

In addition to position guidance, the present invention also has posture guidance, which can achieve a more accurate auxiliary remote operation process and significantly improve the operation accuracy and efficiency.

Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

(1) The remote operation process is accompanied by position guidance. Compared with the traditional guidance method, it takes into account both movement efficiency and movement accuracy, has higher guidance efficiency, and can reduce the burden on operators.

(2) The use of force feedback master hand and six-dimensional force sensor can realize real-time control of the position and posture of the robotic arm, and realize tactile perception when grinding objects. The operation process is more in line with human habits and improves operation efficiency.

(3) Use virtual space to provide stereoscopic visual perception of the workspace, making the operation immersive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of the structure of a polishing robot teleoperation system;

FIG2 is a six-dimensional force sensor calibration posture diagram;

FIG3 is a schematic diagram of workspace matching and coordinate conversion;

FIG4 is a schematic diagram of positioning the polishing target point;

FIG5 is a flow chart of location guidance;

FIG6 is a schematic diagram of position guidance, wherein FIG6(a) is a schematic diagram of a guidance channel, FIG6(b) is a schematic diagram of a cylindrical guidance, and FIG6(c) is a schematic diagram of a funnel guidance;

FIG7 is a schematic diagram of determining the position of the end point of the robot arm in the funnel-shaped guide channel;

FIG8 is a schematic diagram showing the calculation principle of the normal vector of the model surface;

FIG9 is a schematic diagram of a virtual space coordinate system and a robot coordinate system;

FIG10 is a schematic diagram of the conversion process from the virtual space coordinate system to the robot coordinate system;

FIG11 is a schematic diagram of posture guidance.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings.

An embodiment of the present invention provides a polishing robot teleoperation method, which realizes position guidance and posture guidance based on the polishing robot teleoperation system.

As shown in Figure 1, the polishing robot is a robotic arm with a six-dimensional force sensor at the end. The remote control system of the polishing robot includes a force feedback master hand, a host computer, VR glasses and a binocular camera. The force feedback master hand adopts a six-dimensional tactile force input and output device, and the robotic arm adopts a six-joint collaborative robot, both of which are existing technologies. The force feedback master hand is used to control the movement of the robotic arm, and the six-dimensional force sensor is used to sense the contact force at the end of the robotic arm and feed the contact force back to the force feedback master hand.

The polishing robot remote operation method specifically comprises the following steps:

(1) A virtual space including the polishing robot, the object to be polished, and the surrounding environment is established. The virtual space realizes visual feedback through VR glasses; gravity compensation is performed on the six-dimensional force sensor, and the coordinates of the force feedback master hand and the robotic arm are transformed and matched with the workspace, so as to realize the movement operation of the force feedback master hand on the robotic arm.

(101) Obtain the lengths of the joints of the force feedback master hand and the robotic arm, establish a D-H coordinate system, solve the D-H parameter table, and obtain the forward and inverse solution expressions of the force feedback master hand and the robotic arm based on the D-H parameter table.

(102) When establishing a virtual space, the robot arm model, the six-dimensional force sensor model, and the tool model (such as a grinding head) are imported into the virtual space in advance, and then the binocular camera is used to collect point cloud data of the object to be polished and the surrounding environment. The three-dimensional reconstruction of the work scene is realized in the host computer based on the point cloud data, thereby realizing the construction of the virtual space.

(103) Measure the measurement readings of the six-dimensional force sensor in various postures and calibrate the data, and calculate the gravity compensation according to the formula.

When the robot posture changes, the posture of the six-dimensional force sensor will change, affecting the output result. Therefore, it is necessary to perform gravity compensation on the force and torque of the six-dimensional force sensor. Table 1 is the collected six-dimensional force sensor calibration data table.

Table 1 Six-axis force sensor calibration data table

The measurement data of the six-dimensional force sensor includes gravity, acceleration force and contact force. Usually, the robot moves slowly during force control, and the acceleration force can be ignored. In the robot controller, the RPY angle is used to represent the robot coordinate system posture, namely Roll, Pitch, Yam, corresponding to the X, Y, and Z angles in Table 1, which represent the angles of rotation around the Z axis, Y axis, and X axis respectively; Fx, Fy, and Fz are the axial forces during measurement, in N; Tx, Ty, and Tz are the torque forces during measurement, in N·m.

Measure the sensor readings of the six-dimensional force sensor in the six postures shown in Figure 2, calibrate the sensor zero point based on the readings, and calculate the tool gravity and the position of the center of mass. The calculation formula is as follows:

Among them, G is the tool gravity; _Lx , _Ly , and _Lz are the coordinate positions of the center of mass in the sensor coordinate system; F is the measured axial force value, and T is the measured torque value. For example, _Fx1 is the axial force in the x direction when measuring posture 1, and _Tz5 is the torque value in the z direction when measuring posture 5.

By performing gravity compensation on the sensor data, the magnitude of the contact force and contact torque can be obtained.

(104) Collect the force feedback main hand end posture information, perform coordinate transformation on it and match it with the workspace, convert it into the robot arm movement coordinate point, and control the movement of the robot arm.

As shown in Figure 3, the robot arm joints are set to rotate around the previous joint connection point, and the six-dimensional force sensor and tool model are fixed on the last joint of the robot arm. Read the robot arm joint angle sensor data, set the angle of the robot arm component in the virtual space relative to the parent component, and make the virtual robot arm model move synchronously with the real robot arm. The host computer collects the angle of the main hand joint through the sensor, and brings it into the kinematics forward expression to obtain the main hand target point position P1 (x ₁ , y ₁ , z ₁ ) and angle θ1 (θx, θy, θz); perform coordinate conversion on the position and angle and perform workspace matching, convert the main hand space into the workspace (that is, the main hand coordinates are converted into the moving coordinate points of the robot arm in the virtual space), and the ratio of the workspace conversion is K1 (K _X , K _Y , K _Z ).

Combined with Figure 1, at the control end, the operator observes the virtual space by wearing VR glasses, and uses the force feedback master hand to send control instructions to the host computer. The host computer converts the movement of the force feedback master hand in the virtual space into the movement of the mechanical arm in the virtual space to achieve the motion control of the robot. At the controlled end, the robot moves and sends real-time information to the host computer, including the angles of each joint of the robot and the six-dimensional force sensor data, and realizes visual and tactile (force) feedback through the force feedback master hand and VR glasses.

(2) Determine the position of the grinding target point on the surface of the object to be ground in the virtual space.

As shown in Figure 4, after the binocular camera scans the object to be polished, the position of the polishing target point needs to be determined. After the binocular camera is scanned after distortion correction, the three-dimensional size of the object to be polished is known. After scanning, the polishing target point P on the object to be polished is identified. A plane coordinate system is established with the three known corner points O, A and B on the bottom surface of the object to be polished, with the OA direction as the X-axis and the OB direction as the Y-axis; then a spatial coordinate system is established with the direction perpendicular to the OAB surface and toward the polishing target point P as the Z-axis. Point P is translated to the boundary line along the negative direction of the Y-axis and is set as point P'. The line connecting PP' is the coordinate of the Y-axis. A line is drawn from point P' to OA along the negative direction of the Z-axis, which is the coordinate of point P on the Z-axis in the spatial coordinate system. The distance between point O and the line is the coordinate of the X-axis. The coordinate position of point P relative to point O (Px, Py, Pz) is thus obtained.

(3) Calculate the distance between the end point of the robot arm and the grinding target point. If the distance is greater than the distance threshold, execute step (4); otherwise, execute step (5).

According to the virtual space, the position of the grinding target point and the position of the end point of the robot arm are obtained, the distance between the two is calculated, and it is determined whether the robot arm is close to the grinding target point. In this embodiment, the distance threshold is 10% of the length of the robot arm, which is 250mm. If the distance is greater than 250mm, the robot arm is far away from the grinding target point. If the distance is less than or equal to 250mm, the distance between the robot arm and the grinding target point is close.

(4) Construct a cylindrical channel to generate distance-priority virtual force guidance. In the process of controlling the movement of the robot arm by the force feedback master hand, force feedback guidance is performed according to the position of the end point of the robot arm. When the position of the end point of the robot arm is within the cylindrical guidance channel, no force feedback is performed (the guidance force is 0); when the end point of the robot arm exceeds the cylindrical guidance channel, a virtual force guidance is generated in the direction of the point in the cylindrical guidance channel closest to the end point of the robot arm; then return to step (3).

The cylindrical guide channel is generated in the virtual space with the coordinates of the end point of the robot arm as the starting point and the coordinates of the grinding target point as the end point.

Figure 6(a) is a schematic diagram of the guide channel. The calculation formula of the virtual force _Fd of the cylindrical guide channel is:

F _d = k _d δ(X _d )

δ(X _d )＝X _d −D(X _d )

Among them, _Fd is the guiding force vector, _kd is the feedback coefficient of force feedback; δ( _Xd ) is a vector, the direction is the direction from the end point of the robot arm to the axis of the cylindrical guiding channel, and the magnitude is the distance from the end point of the robot arm to the axis of the cylindrical guiding channel; _rd is the radius of the cylindrical guiding channel; _Xd represents the coordinate of the end point of the robot arm in the virtual space, D( _Xd ) represents the point on the guiding path that is closest to the end point of the robot arm; a is a value greater than 0, which is adjusted according to actual conditions.

As shown in Figure 6(b), X _start is the starting position of the end point of the robot arm, and X _end is the position of the current grinding target point. When the guidance starts, a cylindrical guide channel is generated with the line connecting X _start and X _end as the axis and r _d as the radius. X _d is the position of the end point of the robot arm, and F _d is the guiding force vector. When the position of the end point of the robot arm is within the cylindrical guide channel, that is, δ(X _d )≤r _d , no force feedback is performed; when the end point of the robot arm exceeds the cylindrical guide channel, that is, δ(X _d )>r _d , force feedback constraint is performed, and the direction is the point in the cylindrical channel closest to the robot arm coordinates.

(5) Construct a virtual force guide that prioritizes accuracy in generating a funnel-shaped channel. If the end point of the robot arm is in the funnel-shaped channel, generate a virtual force guide toward the central axis and the polishing target point according to the position of the end point of the robot arm. The central axis is the line connecting the end point of the robot arm and the polishing target point. Then return to step (3).

The funnel-shaped guide channel is generated with the line between the end point of the robot arm and the grinding target point as the central axis and the distance as the height, wherein the grinding target point is the top surface and the end point of the robot arm is the bottom surface.

Figure 6(a) is a schematic diagram of the guide channel. The calculation formula of the virtual force _Ff of the funnel-shaped guide channel is:

F _f ＝F _sin +F _cos ＝k _sin δ _sin (X _f )+k _cos δ _cos (X _f )

Among them, F _sin is the force of the sine component of the force feedback at the end of the robotic arm within the funnel range, F _cos is the force of the cosine component of the force feedback at the end of the robotic arm within the funnel range, k _sin is the feedback coefficient of the sine component of the force feedback at the end of the robotic arm within the funnel range, k _cos is the feedback coefficient of the cosine component of the force feedback at the end of the robotic arm within the funnel range; δ _sin (X _f ) is the vector pointing to the funnel axis from the end point of the robotic arm; δ _cos (X _f ) is the vector parallel to the funnel axis from the end point of the robotic arm; X _f is the position of the end point of the robotic arm.

As shown in Figure 6(c), X _start is the starting position of the end point of the robot, X _end is the position of the grinding target point, the central axis of the funnel is the line between X _start and X _end , α = 45° is the angle of the funnel opening (i.e., the funnel opening angle), and r _f = 250 mm is the radius of the bottom of the funnel. If the end point x _f of the robot arm is in the funnel, force feedback is generated to guide the operator to approach the grinding target point, where the guiding force is divided into the sine component force and the cosine component force.

As shown in Figure 7, the method for determining whether the end point of the robot arm is in the funnel-shaped channel is:

Given the position of the end point of the robot arm X _f , the vector δ _sin (X _f ) pointing from the end point of the robot arm to the axis of the funnel and the vector δ(X _f ) pointing from the end point of the robot arm to the grinding target point can be calculated. Since the angle α of the funnel opening is known, the value of sinα can be predetermined. The sine value of the angle between the line connecting the current point of the robot arm and the grinding target point and the center axis of the funnel is calculated by |δ _sin (X _f )|/ _δ (X f ). If the calculated sine value is less than sinα and |δ _sin (X _f )|<r _f , the end point of the robot arm X _f is judged to be within the range of the funnel.

(6) Steps (3) to (5) are executed repeatedly until the grinding target point is reached, as shown in the flowchart of FIG5 .

The embodiment of the present invention divides the guide channel into a cylindrical guide channel and a funnel-shaped guide channel. When the robot arm is far away from the grinding target point, the cylindrical guide channel can be used to quickly approach the grinding target point. When the distance is close, the funnel-shaped guide channel can be used to ensure higher precision.

(7) Determine the normal line at the polishing target point.

As shown in FIG8 , the model of the object to be polished is identified using a virtual space, and the vertical points on the surface of the object to be polished are calculated. In the virtual space, all objects are constructed by models, and the generation of the physical model is created by a series of triangles. Generally, the definition of a physical model is based on data that can determine the three angles of the triangle, and is formed by a set of lines connected to each other in different planes through spatial positions. In order to obtain the direction perpendicular to the object to be polished at the polishing target point, the triangular mesh of the model is used for calculation. In the virtual space, the vertex closest to the polishing target point on the model of the object to be polished is selected as the basic vertex. Since the model is composed of triangles, the basic vertex can definitely form 1 to n triangles with the surrounding vertices. Select one of the triangles, the basic vertex is a, and the other two points are b and c. Given the coordinates of a, b, and c, the coordinates of points b and c are respectively subtracted from the coordinates of the basic vertex a to obtain two vectors Side1 and Side2. The cross product of these two vectors will result in a third vector η perpendicular to the surface. When performing the cross product, you need to use the left-hand rule to determine the order of operations. When looking down from above the surface of the object to be polished (the normal will point outward), the first vector should sweep across the second vector clockwise. If the operation is performed in the wrong direction, the result will be a vector that is perpendicular to the surface but points inward to the object.

Through the three-dimensional coordinates of points a, b, and c, find the two vectors Side1 and Side2:

Side1＝b-a

Side2＝c-a

Take the cross product of two vectors:

η=Side1×Side2=((by _{-a y} )*(c _z -a _z )-(b _z -a _z )*(c _y -a _y ))*i+((b _x -a _x )* (c _z -a _z )-(b _z -a _z )*(c _x -a _c ))*j+((b _x -a _x )*(c _y -a _y )-(b _y -a _y ) *(c _x -a _x ))*k

A third vector η perpendicular to the surface to be polished is obtained, and its direction is the normal direction of the vertex.

(8) Perform coordinate system conversion on the Euler angles of the normal posture, first convert the virtual space coordinate system into the transition coordinate system, and then convert the transition coordinate system into the robot coordinate system; use quaternion operation to avoid the universal lock problem of Euler angles, first calculate the quaternion required to convert the Euler angles of the virtual space coordinate system into the transition coordinate system, then calculate the quaternion of the transition coordinate system rotated into the robot coordinate system, multiply the two quaternions, and obtain the rotation transformation required to convert the Euler angles in the virtual space into the Euler angles in the robot coordinate system;

Since the virtual space coordinate system is a left-handed coordinate system, it needs to be converted into the right-handed coordinate system used by the robot. First, one axis in the left-handed coordinate system in the virtual space is reversed as the right-handed coordinate system for the intermediate transition, and then the transition right-handed coordinate system is rotated 90 degrees to obtain the robot coordinate system.

Specifically, as shown in Figure 9, it is a comparison diagram between the virtual space coordinate system and the robot coordinate system. When the positive direction of the X axis is the same, the positive directions of the Y axis and the Z axis are interchanged, and the positive directions of rotation around the axis are different. The position in the virtual space coordinate system needs to be converted to the robot coordinate system for use. The value of the Euler angle is solved in the virtual space to determine the posture of the grinding head. The coordinates of the virtual scene are used as the reference, and the formula is derived using the right-hand coordinate system. Since the virtual space coordinate system is different from the robot coordinate system, the conversion between data is completed based on the corresponding relationship.

In order to facilitate the calculation of the posture of the robot arm grinding head perpendicular to the surface to be polished, the calculated vertex normal is overlapped with the axis of the tool coordinate system. Since the order of Euler angles in the virtual space coordinate system is Y axis, X axis, and Z axis, the tool coordinate system is overlapped with the normal to obtain the Euler angle in the virtual space coordinate system, where the pitch angle is eulerx, the Yaw angle is eulery, and the Roll angle is eulerz, which is expressed by Euler angles as (eulerx, eulery, eulerz).

As shown in Figure 10, the Euler angle is converted to the robot coordinate system. First, the rotation in the virtual space coordinate system needs to be converted into the rotation in the transition right-hand coordinate system. The X-axis is rotated by eulerx degrees, which is equivalent to a rotation of -eulerx degrees around the Z axis in the transition right-hand coordinate system when the positive rotation direction is considered; the Y-axis is rotated by eulery degrees, which is equivalent to a rotation of -eulery degrees around the Y axis in the transition right-hand coordinate system when the positive rotation direction is considered; the Z-axis is rotated by eulerz degrees, which is equivalent to a rotation of -eulerz degrees around the X axis in the transition right-hand coordinate system when the positive rotation direction is considered.

Calculate the quaternion required to transform the Euler angles of the virtual space coordinate system to the transition coordinate system:

The calculation result in the transition right-hand coordinate system is q _mid = qz*qy*qx. Then the transition right-hand coordinate system is converted to the robot coordinate system, that is, a 90-degree clockwise rotation around the Y axis. In the right-hand coordinate system, counterclockwise rotation is the positive direction of rotation, that is:

The final calculation result in the robot coordinate system is q _end =q _mid *q _sec .

q _end is the rotation transformation required from the virtual space coordinate system to the robot coordinate system.

(9) Virtual force feedback guides the posture, obtains the current posture of the robot arm, subtracts the normal posture from the robot arm posture, and calculates the difference between the two postures; based on the difference, generates a virtual force guidance close to the target posture.

As shown in Figure 11, force feedback is performed to guide the operator according to the posture. After calculating the surface normal of the object to be polished and converting its posture to the robot coordinate system, the current posture of the robot arm is obtained. The difference between the postures of the normal and the robot arm can be calculated by subtracting the posture of the robot arm from the posture of the normal. The difference is multiplied by the feedback coefficient _Kr to obtain the magnitude of the posture feedback force _Fr and generate force feedback to guide the operator to approach the target posture.

Claims (10)

1. A remote operation method for a polishing robot, characterized in that the polishing robot is a mechanical arm with a six-dimensional force sensor at the end, and is controlled and achieves force feedback through a force feedback master hand; the remote operation method comprises: (1) Establish a virtual space including the polishing robot, the object to be polished, and the surrounding environment. The virtual space realizes visual feedback through VR glasses; performs gravity compensation on the six-dimensional force sensor, performs coordinate transformation and workspace matching on the force feedback master hand and the robotic arm, and realizes the movement operation of the force feedback master hand on the robotic arm; (2) determining the position of the grinding target point on the surface of the object to be ground in the virtual space; (3) Calculate the distance between the end point of the robot arm and the grinding target point. If the distance is greater than the distance threshold, execute step (4); otherwise, execute step (5); (4) Construct a virtual force guide with distance priority in the cylindrical channel. When the end point of the robot arm is within the cylindrical guide channel, no force feedback is performed. When the end point of the robot arm exceeds the cylindrical guide channel, a virtual force guide is generated in the direction of the point in the cylindrical guide channel closest to the end point of the robot arm. Then return to step (3). (5) constructing a virtual force guide with a priority on the accuracy of the funnel-shaped channel generation. If the end point of the robot arm is in the funnel-shaped channel, generate a virtual force guide toward the central axis and the polishing target point according to the position of the end point of the robot arm, wherein the central axis is the line connecting the end point of the robot arm and the polishing target point; then return to step (3); (6) Repeat steps (3) to (5) until the grinding target point is reached. 2. The remote operation method of a polishing robot according to claim 1, characterized in that, in step (1), the gravity compensation of the six-dimensional force sensor comprises: Measure the values of the six-dimensional force sensor in different postures, and calculate the tool gravity and the position of the center of mass of the six-dimensional force sensor: Wherein, G is the tool gravity; _Lz , _Ly , _Lz are the coordinate positions of the center of mass in the sensor coordinate system, F is the measured axial force, and T is the measured torque. 3. The remote operation method of a polishing robot according to claim 1 is characterized in that step (2) comprises: establishing a plane coordinate system with three known corner points O, A and B on the bottom surface of the object to be polished, with the OA direction as the X-axis and the OB direction as the Y-axis; then establishing a space coordinate system with the direction perpendicular to OAB and toward the polishing target point P as the Z-axis; translating point P along the negative direction of the Y-axis to the boundary line, set as point P ^′ , and the line connecting PP ^′ is the coordinate of the Y-axis; drawing a line from point P ^′ to OA along the negative direction of the Z-axis, which is the coordinate of point P on the Z-axis in the coordinate system; the distance between point O and the line is the coordinate of the X-axis; thereby obtaining the coordinate position (Px, Py, Pz) of point P relative to point O. 4. The remote operation method of a polishing robot according to claim 1, characterized in that in step (3), the distance threshold is 10% of the length of the robot arm. 5. The grinding robot teleoperation method according to claim 1, characterized in that, in step (4), a cylindrical guide channel is generated in the virtual space according to the coordinates of the end point of the robot arm as the starting point and the coordinates of the grinding target point as the end point; The calculation formula of the virtual force _Fd of the cylindrical guide channel is: F _d = k _d δ(X _d ) δ(X _d )＝X _d −D(X _d ) Wherein, _Fd is the guiding force vector, _kd is the feedback coefficient of force feedback; δ( _Xd ) is a vector, the direction of which is from the end point of the robot arm to the axis of the cylindrical guiding channel, and the magnitude is the distance from the end point of the robot arm to the axis of the cylindrical guiding channel; _rd is the radius of the cylindrical guiding channel; _Xd represents the coordinate of the end point of the robot arm in the virtual space, D( _Xd ) represents the point on the guiding path that is closest to the end point of the robot arm; a is a value greater than 0. 6. The remote operation method of a polishing robot according to claim 1, characterized in that, in step (5), the funnel-shaped guide channel is generated with the line between the end point of the robot arm and the polishing target point as the central axis and the distance as the height, wherein the polishing target point is the top surface and the end point of the robot arm is the bottom surface; The calculation formula of the virtual force _Ff of the funnel-shaped guide channel is: F _f ＝F _sin +F _cos ＝k _sin δ _sin (X _f )+k _cos δ _cos (X _f ) F _sin is the force of the sine component of the force feedback at the end of the robotic arm within the funnel range, F _cos is the force of the cosine component of the force feedback at the end of the robotic arm within the funnel range, k _sin is the feedback coefficient of the sine component of the force feedback at the end of the robotic arm within the funnel range, k _cos is the feedback coefficient of the cosine component of the force feedback at the end of the robotic arm within the funnel range; δ _sib (X _f ) is the vector pointing to the axis of the funnel from the end point of the robotic arm; δ _cos (X _f ) is the vector parallel to the axis of the funnel from the end point of the robotic arm; X _f is the position of the end point of the robotic arm. 7. The remote operation method of a polishing robot according to claim 6, characterized in that in step (5), the method for determining whether the end point of the robot arm is within the funnel-shaped channel is: Obtain the vector δ _sin (X _f ) from the end point of the robot arm to the funnel axis and the vector δ (X _f ) from the end point of the robot arm to the polishing target point; The sine value of the angle between the line connecting the current point of the robot arm and the grinding target point and the central axis of the funnel is calculated by |δ _sin (X _f )|/δ(X _f ). If the calculated sine value is less than sinα and |δ _sin (X _f )|<r _f , it is judged that the end point X _f of the robot arm is within the range of the funnel; α is the funnel opening angle, and r _f is the radius of the bottom of the funnel. 8. The remote operation method of a polishing robot according to any one of claims 1 to 7, characterized in that it further comprises: (7) Determine the normal line at the polishing target point; (8) Perform coordinate system conversion on the Euler angles of the normal posture, first convert the virtual space coordinate system into the transition coordinate system, and then convert the transition coordinate system into the robot coordinate system; use quaternion operation to avoid the universal lock problem of Euler angles, first calculate the quaternion required to convert the Euler angles of the virtual space coordinate system into the transition coordinate system, then calculate the quaternion of the transition coordinate system rotated into the robot coordinate system, multiply the two quaternions, and obtain the rotation transformation required to convert the Euler angles in the virtual space into the Euler angles in the robot coordinate system; (9) Virtual force feedback guides the posture, obtains the current posture of the robot arm, subtracts the normal posture from the robot arm posture, and calculates the difference between the two postures; based on the difference, generates a virtual force guidance close to the target posture. 9. The remote operation method of a polishing robot according to claim 8 is characterized in that step (7) includes: selecting the vertex on the model of the object to be polished in the virtual space that is closest to the polishing target point as the basic vertex a, and obtaining the other two points b and c that form a triangle with the basic vertex a; subtracting the coordinates of the basic vertex a from the coordinates of points b and c respectively to obtain two vectors Side1 and Side2; performing a cross product on the two vectors to obtain a third vector η that is perpendicular to the two vectors, and the direction of the third vector η is the normal direction at the polishing target point. 10. The remote operation method of a polishing robot according to claim 8, characterized in that step (8) comprises: calculating the quaternion q _mid required to convert the Euler angle of the virtual space coordinate system into the transition coordinate system: q _mid = qz*qy*qx Among them, (eulerx, eulery, eulerz) is the Euler angle in the virtual space coordinate system; Calculate the quaternion q _sec of the transition coordinate system rotation to the robot coordinate system: The rotation transformation required from the virtual space coordinate system to the robot coordinate system is: q _end =q _mid *q _sec .