Methods for shaft and spline mating in the flexible assembly process of parallel platforms

Abstract

This invention discloses a method for aligning the axis and spline during the flexible assembly process of a parallel platform. The method includes the following steps: S1, using a target ball to calibrate the end face of the low-voltage turbine shaft tooling and the end face of the compartment tooling to determine the reference coordinates of the end face of the low-voltage turbine shaft tooling and the end face of the compartment tooling; S2, establishing a predetermined distance between the bottom of the low-voltage turbine shaft and the top of the compartment, and using this position as the reference position; S3, using a laser tracker to measure the position of each target point at the reference position, moving the parallel platform to obtain the positions of the end face of the low-voltage turbine shaft tooling and the end face of the compartment tooling; establishing a low-voltage turbine shaft coordinate system {D} and a compartment coordinate system {C}; S4, correcting based on the actual measurement results to obtain the homogeneous transformation matrix between the low-voltage turbine shaft coordinate system {D} and the compartment coordinate system {C}, and adjusting the compartment axis according to the homogeneous transformation matrix; S5, using impedance control during the contact between the spline and the spline groove, rotating the compartment to align the spline inside the engine with the spline groove at the end of the low-voltage turbine shaft.

Description

Technical Field

[0001] This invention discloses a flexible assembly method for parallel platforms oriented towards low-power turboshaft engines, relating to the fields of engine assembly and compliant control technology for parallel platforms. Background Technology

[0002] With rapid societal development, the machinery manufacturing industry is constantly progressing, and manufacturing technologies are continuously innovating. In the manufacturing process of aero-engines, assembly is an indispensable part, involving the assembly and disassembly of all components, accessories, parts, units, main units, and the entire engine. Traditionally, the assembly of the low-voltage turboshaft in engines is done manually, using a crane to lift the low-voltage turboshaft, with multiple operators holding it and assembling it. The entire process requires operators to have extensive experience and skills; even slight carelessness can lead to product damage, and in severe cases, even injuries such as pinching or crushing to operators. Furthermore, the crane only provides auxiliary support and cannot guarantee the precision of the spline fit. The entire assembly process lacks a safe, high-precision, and efficient method. Summary of the Invention

[0003] To address the above problems, this invention proposes an automatic compliant assembly method for parallel platforms in engine low-profile turboshaft assembly. By implementing compliant control on the parallel platform, the assembly process can be made more flexible, efficient, and precise, transforming traditional manual assembly into automated assembly.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a method for the fit between the shaft and spline during the flexible assembly process of a parallel platform, the method comprising the following steps:

[0005] S1. Use a target ball to calibrate the end face of the low-pressure turbine shaft tooling and the end face of the compartment tooling. Use a laser tracker to measure the three-dimensional coordinates of the target ball in space to determine the reference coordinates of the end face of the low-pressure turbine shaft tooling and the end face of the compartment tooling.

[0006] S2, set the radial rotation center of the low-pressure turbine shaft to coincide with the rotation axis of the end rotary motor in the low-pressure turbine shaft tooling, so that the bottom of the low-pressure turbine shaft is at a set distance from the top of the compartment, and use this position as the reference position.

[0007] S3. At the reference position, use a laser tracker to measure the position of each target point, move the parallel platform to obtain the position of the end face of the low-vortex shaft tool and the end face of the compartment tool. The parallel platform is a parallel robot connected to the end of the low-vortex shaft tool. The parallel robot is used to realize the movement of the low-vortex shaft in six directions. Establish the low-vortex shaft coordinate system {D} and the compartment coordinate system {C}.

[0008] S4. Based on the actual measurement results, a correction is made to obtain the homogeneous transformation matrix between the low-vortex axis coordinate system {D} and the compartment coordinate system {C}. According to the homogeneous transformation matrix Adjust the axis of the compartment section;

[0009] S5 utilizes impedance control to rotate the compartment during the contact between the spline and the spline groove, aligning the spline inside the engine with the spline groove at the end of the low-power turbine shaft.

[0010] Furthermore, step S1 specifically includes:

[0011] Three fixed target mounts are installed on the low-pressure turbine shaft fixture and the compartment fixture, respectively. These targets must be detectable by the laser tracker within the calibration range and not be aligned in a straight line. The three-dimensional coordinates of the three target spheres, i.e., the three-dimensional coordinates of points O, A, and B, are set. The specific steps for establishing the coordinate system are as follows:

[0012] S11, take point O as the origin of the coordinate system;

[0013] S12, draw a ray from point O to point A, and set... As the positive X-axis of the coordinate system;

[0014] S13, draw a ray from point O to point B, with... and The surface formed by the intersection is used as the XY plane of the coordinate system;

[0015] S14, Taking point B as a point on the positive Y-axis of the coordinate system, draw a line in the XY plane starting from O, intersecting the positive Y-axis... A vertical ray is used as the positive Y-axis of the coordinate system;

[0016] S15, determine the Z-axis of the coordinate system using the right-hand rule.

[0017] Furthermore, at the reference position, a laser tracker is used to measure the position of each target point to obtain the position of the end face of the low-pressure turbine shaft tooling and the end face of the compartment tooling, specifically:

[0018] S31, move the parallel platform a certain distance in the positive X-axis direction, and measure the position after it comes to rest. Record this as... ;

[0019] S32, cause the parallel platform to translate a certain distance in the positive Y-axis direction, and measure the position after it comes to rest, denoted as... ;

[0020] S33, the parallel platform returns to the reference position, causing the end rotary motor to move. After each set angle of rotation, the position at that moment is recorded. This process is repeated n times and recorded as follows: … , n≥2;

[0021] S34, utilizing , … Create a spatial circle I, with the center of circle I as the origin. As the X-axis Establish the gripper coordinate system {J} with the Y-axis as the Y-axis;

[0022] S35, fix the target at the end of the low-pressure vortex shaft and measure it, denoted as E. Calculate the distance from point E to circle I, denoted as... Remove target thickness and target ball thickness The length of the low-level vortex shaft end was then obtained. Translation with the positive Z-axis of the parallel platform coordinate system as the direction of movement. This yields the TCP coordinate system {H}.

[0023] S36, adjust the attitude of the parallel platform and measure the target point and the six-dimensional force sensor values ​​while stationary, repeat m times, where the point is denoted as . … The force value is denoted as … The torque value is denoted as … ; using E, … Establish a spatial sphere Q, and translate the origin of the gripper coordinate system {J} to the center of sphere Q to establish a parallel platform coordinate system {P}.

[0024] Furthermore, the method also includes impedance control of the parallel platform using a six-dimensional force sensor installed at the end of the low-pressure vortex shaft tooling. The specific implementation process is as follows:

[0025] The parallel platform is simulated as a mass-spring-damped system, and its control law is:

[0026]

[0027] in , , These represent mass, damping, and stiffness, respectively, with subscripts. Represents the expected value of the system. This indicates the force applied to the end of the parallel platform; the parameters are calibrated according to the actual environment.

[0028] A six-dimensional force sensor is used to measure the forces and torques in three directions of the low-pressure worm gear tooling as the external contact force input for impedance control. Its components are as follows:

[0029]

[0030]

[0031] in , These are measurements from a six-dimensional force sensor. , The force and torque exerted by the load gravity on the six-dimensional force sensor. , For the zero point of the six-dimensional force sensor, , This refers to the force and torque exerted by external forces on a six-dimensional force sensor; utilizing... … and … Calculations were performed to obtain , , , Thus, the external force can be obtained by the following formula:

[0032] ;

[0033] ;

[0034] Impedance control is applied to the parallel platform based on external forces. If a keyway misfit occurs when the parallel platform moves downwards, Increase, at this time maintain contact force and rotate the low vortex shaft, when monitored When the speed decreases, the keyway fit is considered complete, and rotation stops; simultaneously, impedance control is based on... Rotating Parallel Platform This avoids excessive torque between the tooth grooves.

[0035] Furthermore, real-time monitoring , , , Control the X, Y, and Y axes of the parallel platform respectively. , Moving in the TCP coordinate system {H} allows the parallel platform to automatically adjust the position of the axis according to the force applied to the end.

[0036] Furthermore, impedance control is based on Rotating Parallel Platform During the process, the X, Y, and E coordinates of the parallel platform are determined according to the TCP coordinate system {H} of the parallel platform. , Motion control quantity.

[0037] Furthermore, in step 3, the parallel platform motion coordinate system {P} is converted into the TCP coordinate system {H} to ensure that the bottom of the low-pressure vortex shaft does not move much when the parallel platform rotates, thus avoiding collisions inside the compartment.

[0038] The flexible assembly method for parallel platforms oriented towards low-vortex shafts provided in this invention has the following main advantages:

[0039] The parallel platform can achieve an accuracy of 0.05mm, and the accuracy can be guaranteed when combined with force control; only one person is needed to control the start and stop of the automatic process and monitor the assembly data, without having to follow the product throughout the process; workers do not need to enter the assembly area, thus improving safety. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0041] Figure 1 This is a flowchart illustrating the coordinate system establishment process in the embodiment.

[0042] Figure 2 A schematic diagram of the rotation center calibration method;

[0043] Figure 3 This is a schematic diagram of the coordinate system;

[0044] Figure 4 Schematic diagram of laser tracker adjustment principle;

[0045] Figure 5 This is a schematic diagram of the hole-shaft mating process;

[0046] Figure 6 Schematic diagram of auxiliary assembly equipment for low-voltage turbine shafts;

[0047] Figure 7 This is a schematic diagram of an intelligent assembly platform;

[0048] Figure 8 This is a schematic diagram of the overall layout of the device;

[0049] Figure 9 System topology diagram;

[0050] Figure 10 A cross-sectional view showing the keyway assembly process;

[0051] Figure 11 Diagram of the compliant control model;

[0052] Figure 12 This is a flowchart of the laser tracker's workflow. Detailed Implementation

[0053] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention. Other embodiments obtained by those skilled in the art based on the present invention without creative effort are all within the protection scope of the present invention.

[0054] This application first introduces a parallel platform flexible assembly system for low-turbine shafts. The system includes: low-turbine shaft auxiliary assembly equipment and an intelligent assembly platform. The low-turbine shaft auxiliary assembly equipment is used for the movement of the low-turbine shaft section, and the intelligent assembly platform is used for the fixation of the compartment section.

[0055] The intelligent assembly platform includes a section tooling seat, a section lifting shaft is provided on the section tooling seat, a section tooling arm is provided on the section lifting shaft, the section tooling arm can move vertically on the section lifting shaft, and the section tooling arm is a section tooling clamping part.

[0056] The low-profile turboshaft auxiliary assembly equipment includes a clamping and attitude adjustment unit, a compliant force control unit, and a calibration unit. The clamping and attitude adjustment unit is used for all movements during the assembly process except for force control. The compliant force control unit is used for the force control movement of the system. It uses the impedance control algorithm in the PLC with the contact force as input to realize the flexible attitude adjustment of the low-profile turboshaft during assembly. The calibration unit uses a laser tracker to align the axis of the low-profile turboshaft with the axis of the engine compartment section.

[0057] The low-turbine shaft auxiliary assembly includes a base with a base rotation axis in the horizontal direction for rotating the entire base horizontally. The base also has a low-turbine shaft lifting axis in the vertical direction for lifting the boom vertically. The boom is mounted on the low-turbine shaft lifting axis. The end of the boom is a parallel platform, which is connected to a six-dimensional force sensor and grippers. The grippers are equipped with low-turbine shaft fixtures, and the position and orientation of the fixtures are controlled by the sensor and grippers.

[0058] Furthermore, the clamping and attitude adjustment unit includes an attitude adjustment robotic arm, a compartment gripper, and a compartment rotary motor connected in sequence. The clamping and attitude adjustment unit is equipped with five compartment rotary motors, which are used to realize the lifting, rotation, translation, opening and closing of the attitude adjustment robotic arm, and axial rotation of the gripper and the low-profile vortex shaft, respectively. The low-profile vortex shaft is assembled with the spline and spline groove on the compartment through axial rotation.

[0059] Furthermore, the calibration unit is equipped with a system that installs target balls on the tooling of the compartment and on the upper surface of the low-pressure vortex shaft, respectively, and tracks the spatial position of the target balls with a laser tracker to obtain the relative coordinate system relationship between the low-pressure vortex shaft and the compartment, outputs the fine-tuned displacement angle, and guides the movement of the parallel platform.

[0060] Furthermore, the compliant force control unit is equipped with a PLC, a six-dimensional force sensor, and a parallel platform. The PLC takes the contact force as input and realizes the flexible posture adjustment of the low-profile worm shaft during assembly through an impedance control algorithm. The force value fed back by the six-dimensional force sensor is used as input, and the displacement value of the parallel platform is used as output.

[0061] As a preferred embodiment of this application, the parallel platform is a parallel robot, a composite motion device consisting of 6 motors, electrically connected to the PLC, to realize the movement of the low-profile vortex shaft in six directions: X, Y, Z, RX, RY, and RZ.

[0062] Example 1

[0063] Based on the above-mentioned flexible assembly system, the method for shaft and spline mating during the flexible assembly process of the parallel platform provided in this embodiment of the invention includes the following steps:

[0064] S1. Use a target ball to calibrate the end face of the low-pressure turbine shaft tooling and the end face of the compartment tooling. Use a laser tracker to measure the three-dimensional coordinates of the target ball in space to determine the reference coordinates of the end face of the low-pressure turbine shaft tooling and the end face of the compartment tooling.

[0065] S2, set the radial rotation center of the low-pressure turbine shaft to coincide with the rotation axis of the end rotary motor in the low-pressure turbine shaft tooling, so that the bottom of the low-pressure turbine shaft is at a set distance from the top of the compartment, and use this position as the reference position.

[0066] S3. At the reference position, use a laser tracker to measure the position of each target point, move the parallel platform to obtain the position of the end face of the low-vortex shaft tool and the end face of the compartment tool. The parallel platform is a parallel robot connected to the end of the low-vortex shaft tool. The parallel robot is used to realize the movement of the low-vortex shaft in six directions. Establish the low-vortex shaft coordinate system {D} and the compartment coordinate system {C}.

[0067] S4. Based on the actual measurement results, a correction is made to obtain the homogeneous transformation matrix between the low-vortex axis coordinate system {D} and the compartment coordinate system {C}. According to the homogeneous transformation matrix Adjust the axis of the compartment section;

[0068] S5 utilizes impedance control to rotate the compartment during the contact between the spline and the spline groove, aligning the spline inside the engine with the spline groove at the end of the low-power turbine shaft.

[0069] Furthermore, step S1 specifically includes:

[0070] Three fixed target mounts are installed on the low-pressure turbine shaft fixture and the compartment fixture, respectively. These targets must be detectable by the laser tracker within the calibration range and not be aligned in a straight line. The three-dimensional coordinates of the three target spheres, i.e., the three-dimensional coordinates of points O, A, and B, are set. The specific steps for establishing the coordinate system are as follows:

[0071] S11, take point O as the origin of the coordinate system;

[0072] S12, draw a ray from point O to point A, and set... As the positive X-axis of the coordinate system;

[0073] S13, draw a ray from point O to point B, with... and The surface formed by the intersection is used as the XY plane of the coordinate system;

[0074] S14, Taking point B as a point on the positive Y-axis of the coordinate system, draw a line in the XY plane starting from O, intersecting the positive Y-axis... A vertical ray is used as the positive Y-axis of the coordinate system;

[0075] S15, determine the Z-axis of the coordinate system using the right-hand rule.

[0076] Furthermore, at the reference position, a laser tracker is used to measure the position of each target point to obtain the position of the end face of the low-pressure turbine shaft tooling and the end face of the compartment tooling, specifically:

[0077] S31, move the parallel platform a certain distance in the positive X-axis direction, and measure the position after it comes to rest. Record this as... ;

[0078] S32, cause the parallel platform to translate a certain distance in the positive Y-axis direction, and measure the position after it comes to rest, denoted as... ;

[0079] S33, the parallel platform returns to the reference position, causing the end rotary motor to move. After each set angle of rotation, the position at that moment is recorded. This process is repeated n times and recorded as follows: … , n≥2;

[0080] S34, utilizing , … Create a spatial circle I, with the center of circle I as the origin. As the X-axis Establish the gripper coordinate system {J} with the Y-axis as the Y-axis;

[0081] S35, fix the target at the end of the low-pressure vortex shaft and measure it, denoted as E. Calculate the distance from point E to circle I, denoted as... Remove target thickness and target ball thickness The length of the low-level vortex shaft end was then obtained. Translation with the positive Z-axis of the parallel platform coordinate system as the direction of movement. This yields the TCP coordinate system {H}.

[0082] S36, adjust the attitude of the parallel platform and measure the target point and the six-dimensional force sensor values ​​while stationary, repeat m times, where the point is denoted as . … The force value is denoted as … The torque value is denoted as … ; using E, … Establish a spatial sphere Q, and translate the origin of the gripper coordinate system {J} to the center of sphere Q to establish a parallel platform coordinate system {P}.

[0083] Furthermore, the method also includes impedance control of the parallel platform using a six-dimensional force sensor installed at the end of the low-pressure vortex shaft tooling. The specific implementation process is as follows:

[0084] The parallel platform is simulated as a mass-spring-damped system, and its control law is:

[0085]

[0086] in , , These represent mass, damping, and stiffness, respectively, with subscripts. Represents the expected value of the system. This indicates the force applied to the end of the parallel platform; the parameters are calibrated according to the actual environment.

[0087] A six-dimensional force sensor is used to measure the forces and torques in three directions of the low-pressure worm gear tooling as the external contact force input for impedance control. Its components are as follows:

[0088]

[0089]

[0090] in , These are measurements from a six-dimensional force sensor. , The force and torque exerted by the load gravity on the six-dimensional force sensor. , For the zero point of the six-dimensional force sensor, , This refers to the force and torque exerted by external forces on a six-dimensional force sensor; utilizing... … and … Calculations were performed to obtain , , , Thus, the external force can be obtained by the following formula:

[0091] ;

[0092] ;

[0093] Impedance control is applied to the parallel platform based on external forces. If a keyway misfit occurs when the parallel platform moves downwards, Increase, at this time maintain contact force and rotate the low vortex shaft, when monitored When the speed decreases, the keyway fit is considered complete, and rotation stops; simultaneously, impedance control is based on... Rotating Parallel Platform This avoids excessive torque between the tooth grooves.

[0094] Furthermore, real-time monitoring , , , Control the X, Y, and Y axes of the parallel platform respectively. , Moving in the TCP coordinate system {H} allows the parallel platform to automatically adjust the position of the axis according to the force applied to the end.

[0095] Furthermore, impedance control is based on Rotating Parallel Platform During the process, the X, Y, and E coordinates of the parallel platform are determined according to the TCP coordinate system {H} of the parallel platform. , Motion control quantity.

[0096] Furthermore, in step 3, the parallel platform motion coordinate system {P} is converted into the TCP coordinate system {H} to ensure that the bottom of the low-pressure vortex shaft does not move much when the parallel platform rotates, thus avoiding collisions inside the compartment.

[0097] To ensure the reliability and accuracy of the entire automated process, the key challenges were analyzed and addressed. These challenges primarily lie in axis alignment and spline fit. This application's technical solution utilizes a laser tracker and a six-dimensional force sensor in conjunction with a parallel platform to resolve these issues.

[0098] 1. Coordinate system calibration

[0099] A laser tracker can measure the three-dimensional coordinates of a target sphere in space with an accuracy of up to 0.03 mm. In three-dimensional space, a spatial coordinate system can be determined using the spatial coordinates of three points. Assuming the three-dimensional coordinates of the three target spheres (point O, point A, point B) have been measured, the specific steps for establishing the coordinate system are as follows:

[0100] 1) Take point O as the origin of the coordinate system.

[0101] 2) Draw a ray from point O to point A. The positive X-axis of the coordinate system

[0102] 3) Draw a ray from point O to point B. and The surface formed by the intersection serves as the XY plane of the coordinate system.

[0103] 4) Treat point B as a point on the positive Y-axis of the coordinate system. In the XY plane, starting from O, draw a line that intersects the positive Y-axis with the positive Y-axis. A perpendicular ray, representing the positive Y-axis of the coordinate system.

[0104] 5) Determine the Z-axis of the coordinate system using the right-hand rule.

[0105] like Figure 2 The diagram shows the steps involved in determining the coordinate system.

[0106] Three fixed target seats are installed on the low-pressure turbine shaft fixture and the compartment fixture respectively. They are required to be detectable by the laser tracker within the calibration range and not be on a straight line.

[0107] Calibration requires an accurate reference target, so the robotic arm is first moved in a jogging motion to position the low-pressure turbine shaft directly above the compartment and insert a portion of it into the bore. Due to the characteristics of the equipment, it can be assumed that the radial rotation center of the low-pressure turbine shaft and the rotation axis of the end-effector motor coincide.

[0108] To ensure product safety and prevent collisions between the low-profile vortex shaft and the compartment, a dial indicator is used for measurement. The dial indicator is fixed to the upper surface of the compartment, with the probe in contact with the low-profile vortex shaft. The end-rotor motor is slowly moved, and the parallel platform is finely adjusted based on the dial indicator reading until the dial indicator reading shows no significant fluctuation during rotation. Figure 2 As shown.

[0109] Return the rotary motor to the zero position, and move the robotic arm vertically upward to create a distance between the bottom of the low-pressure turbine shaft and the top of the compartment. Use this position as the reference point.

[0110] At the reference position, a laser tracker is used to measure the target point, which is denoted as [reference point]. , , The markings on the cabin section tooling are as follows , , Based on the coordinate system establishment method, establish the low-vortex axis coordinate system {D} and the compartment coordinate system {C}.

[0111] A parallel platform coordinate system and a TCP coordinate system are established using a laser tracker, with the laser tracker providing real-time tracking during the process. :

[0112] 1) Move the parallel platform a certain distance in the positive X-axis direction, and measure the position after it comes to rest. Record this position as... ;

[0113] 2) Move the parallel platform a certain distance in the positive Y-axis direction, and measure the position after it comes to rest. Record this position as... ;

[0114] 3) The parallel platform returns to the reference position, causing the end rotary motor to move. After rotating a certain angle, record the position at that point. Repeat n (≥2) times, and record it as _____. … ;

[0115] 4) Utilize , … Create a spatial circle I, with the center of circle I as the origin. As the X-axis Establish the gripper coordinate system {J} with the Y-axis as the Y-axis;

[0116] 5) Fix the target at the end of the low-pressure vortex shaft and measure it, denoted as E. Calculate the distance from point E to circle I, denoted as . Remove target thickness and target ball thickness Then, the length of the low-level vortex shaft end was obtained. The translation is performed with the positive Z-axis of the parallel platform coordinate system as the direction of movement. This yields the TCP coordinate system {H}.

[0117] 6) Adjust the attitude of the parallel platform and measure the target position and the value of the six-dimensional force sensor when it is stationary. Repeat this process m (≥3) times, and record the position as... … The force value is denoted as … (1x3 matrix), the torque value is denoted as … (1x3 matrix). Using E, … Establish a spatial sphere Q, and translate the protocenter of the gripper coordinate system {J} to the center of sphere Q to establish a parallel platform coordinate system {P}.

[0118] The relationship between coordinate systems is as follows Figure 4 As shown.

[0119] The motion coordinate system of the parallel platform is transformed from {P} to the TCP coordinate system {H} to ensure that the movement of the bottom of the low-pressure vortex shaft is not large when the parallel platform rotates, thus avoiding collisions inside the compartment.

[0120] 2. Axis alignment

[0121] During formal assembly, gear backlash and other factors may cause some error in the module axis, necessitating correction based on actual measurement results. Once the low-pressure turbine shaft reaches the reference position, a measurement coordinate system is established between the low-pressure turbine shaft and the module using a laser tracker, denoted as {D'} and {C'}. The homogeneous transformation matrix between them is denoted as... (4x4 matrix). Based on the calibration results, the homogeneous transformation matrix between the low-vortex axis coordinate system {D} and the compartment coordinate system {C} can be obtained. ,Right now

[0122]

[0123]

[0124] If we consider {D'} and {D} as the same coordinate system, then we can obtain

[0125]

[0126] Organizing can yield

[0127]

[0128] Will This is converted into pose adjustment, i.e., the pose adjustment amount of the parallel platform.

[0129] 3. Spline combination

[0130] Due to the unique shape of the spline, a specific angle is required to achieve the proper fit between the spline and the keyway. Assuming the spline has 60 teeth, a maximum axial rotation of ±3° is needed to align the teeth. Therefore, a rotary motor is required during assembly to find the appropriate angle.

[0131] On the other hand, since the low-profile turbine shaft needs to be assembled at the bottom of the compartment, the observation space is narrow and it is impossible to determine the completion of the keyway mating by visual means. Therefore, in order to ensure the safety of the assembly, a six-dimensional force sensor installed at the end is used to control the parallel platform with impedance to monitor and control the assembly force.

[0132] Impedance control is a type of compliant control. This method simulates the end of the parallel platform as a mass-spring-damped system, and its control law is:

[0133]

[0134] in , , These represent mass (inertia), damping, and stiffness, respectively, with subscripts. Represents the expected value of the system. This indicates the force applied to the end of the parallel platform, and the parameters are calibrated according to the actual environment.

[0135] Impedance control uses external contact force as input, therefore it requires identification of the external force. A six-dimensional force sensor can measure force and torque in three directions, and its components are as follows:

[0136]

[0137]

[0138] in , These are measurements from a six-dimensional force sensor. , The force and torque exerted by the load gravity on the six-dimensional force sensor. , For the zero point of the six-dimensional force sensor, , This represents the force and torque exerted on the six-dimensional force sensor by external forces. Gravity compensation is performed using the least squares method. … and … Calculations can be performed to obtain , , , Thus, the external force can be obtained by the following formula.

[0139]

[0140]

[0141] Impedance control is applied to the parallel platform based on external forces. If a keyway misfit occurs when the parallel platform moves downwards, It will increase, at this time maintain the contact force and use the rotary motor to rotate the low vortex shaft, when monitored When the speed decreases, the keyway fit is considered complete, and rotation stops. Simultaneously, impedance control will be adjusted accordingly. Rotating Parallel Platform This avoids excessive torque between the tooth grooves.

[0142] On the other hand, the spline itself has a certain height. If the deviation between the low-profile worm shaft and the spline groove axis is too large, jamming will occur, which in severe cases can lead to product damage. Figure 5 As shown in (a). To ensure that the contact force between the shaft and the hole remains stable within a certain range during this process, monitoring is performed. , , , Control the X, Y, and Y axes of the parallel platform respectively. , Moving in the TCP coordinate system {H} allows the parallel platform to automatically adjust the axis position according to the force applied to the end effector, such as... Figure 5 As shown in (b).

Claims

1. A method for aligning shafts and splines during the flexible assembly process of a parallel platform, characterized in that, The method includes the following steps: S1. Use a target ball to calibrate the end face of the low-pressure turbine shaft tooling and the end face of the compartment tooling. Use a laser tracker to measure the three-dimensional coordinates of the target ball in space to determine the reference coordinates of the end face of the low-pressure turbine shaft tooling and the end face of the compartment tooling. S2, set the radial rotation center of the low-pressure turbine shaft to coincide with the rotation axis of the end rotary motor in the low-pressure turbine shaft tooling, so that the bottom of the low-pressure turbine shaft is at a set distance from the top of the compartment, and use this position as the reference position. S3. At the reference position, use a laser tracker to measure the position of each target point, move the parallel platform to obtain the position of the end face of the low-vortex shaft tool and the end face of the compartment tool. The parallel platform is a parallel robot connected to the end of the low-vortex shaft tool. The parallel robot is used to realize the movement of the low-vortex shaft in six directions. Establish the low-vortex shaft coordinate system {D} and the compartment coordinate system {C}. S4. Based on the actual measurement results, a correction is made to obtain the homogeneous transformation matrix between the low-vortex axis coordinate system {D} and the compartment coordinate system {C}. According to the homogeneous transformation matrix Adjust the axis of the compartment section; S5 utilizes impedance control to rotate the compartment during the contact between the spline and the spline groove, aligning the spline inside the engine with the spline groove at the end of the low-pressure turbine shaft. The specific process of S5 includes impedance control of the parallel platform using a six-dimensional force sensor installed at the end of the low-profile vortex shaft tooling. The specific implementation process is as follows: The parallel platform is simulated as a mass-spring-damped system, and its control law is: ； in , , These represent mass, damping, and stiffness, respectively, with subscripts. This represents the expected value of the system. This indicates the force applied to the end of the parallel platform; the parameters are calibrated according to the actual environment. A six-dimensional force sensor is used to measure the forces and torques in three directions of the low-pressure worm gear tooling as the external contact force input for impedance control. Its components are as follows: ； ； in , These are measurements from a six-dimensional force sensor. , The force and torque exerted by the load gravity on the six-dimensional force sensor. , For the zero point of the six-dimensional force sensor, , The force and torque acting on the six-dimensional force sensor are measured by external forces; using … and … Calculations were performed to obtain , , , Thus, the external force can be obtained by the following formula: ； ； Impedance control is applied to the parallel platform based on external forces. If a keyway misfit occurs when the parallel platform moves downwards, Increase, while maintaining contact force and rotating the low-vortex shaft, when monitored When the speed decreases, the keyway fit is considered complete, and rotation stops; simultaneously, impedance control is based on... Rotating Parallel Platform This avoids excessive torque between the tooth grooves.

2. The method for shaft and spline mating during the flexible assembly process of a parallel platform according to claim 1, characterized in that, Step S1 specifically involves: Three fixed target mounts are installed on the low-pressure turbine shaft fixture and the compartment fixture, respectively. These targets must be detectable by the laser tracker within the calibration range and not be aligned in a straight line. The three-dimensional coordinates of the three target spheres, i.e., the three-dimensional coordinates of points O, A, and B, are set. The specific steps for establishing the coordinate system are as follows: S11, take point O as the origin of the coordinate system; S12, draw a ray from point O to point A, and set... As the positive X-axis of the coordinate system; S13, draw a ray from point O to point B, with... and The surface formed by the intersection is used as the XY plane of the coordinate system; S14, Taking point B as a point on the positive Y-axis of the coordinate system, draw a line in the XY plane starting from O, intersecting the positive Y-axis... A vertical ray is used as the positive Y-axis of the coordinate system; S15, determine the Z-axis of the coordinate system using the right-hand rule.

3. The method for shaft and spline mating during the flexible assembly process of a parallel platform according to claim 1, characterized in that, At the aforementioned reference position, a laser tracker is used to measure the position of each target point to obtain the positions of the low-pressure turbine shaft tooling end face and the compartment tooling end face, specifically: S31, move the parallel platform a certain distance in the positive X-axis direction, and measure the position after it comes to rest. Record this as... ; S32, cause the parallel platform to translate a certain distance in the positive Y-axis direction, and measure the position after it comes to rest, denoted as... ; S33, the parallel platform returns to the reference position, causing the end rotary motor to move. After each set angle of rotation, the position at that moment is recorded. This process is repeated n times and recorded as follows: … , n≥2; S34, utilizing , … Create a spatial circle I, with the center of circle I as the origin. As the X-axis Establish the gripper coordinate system {J} with the Y-axis as the Y-axis; S35, fix the target at the end of the low-pressure vortex shaft and measure it, denoted as E. Calculate the distance from point E to circle I, denoted as... Remove target thickness and target ball thickness The length of the low-level vortex shaft end was then obtained. Translation with the positive Z-axis of the parallel platform coordinate system as the direction of movement. This yields the TCP coordinate system {H}. S36, adjust the attitude of the parallel platform and measure the target point and the six-dimensional force sensor values ​​while stationary, repeat m times, where the point is denoted as . … The force value is denoted as … The torque value is denoted as … ; using E, … Establish a spatial sphere Q, and translate the origin of the gripper coordinate system {J} to the center of sphere Q to establish a parallel platform coordinate system {P}.

4. The method for shaft and spline mating during the flexible assembly process of a parallel platform according to claim 1, characterized in that, Real-time monitoring , , , Control the X, Y, and Y axes of the parallel platform respectively. , Moving in the TCP coordinate system {H} allows the parallel platform to automatically adjust the position of the axis according to the force applied to the end.

5. The method for shaft and spline mating during the flexible assembly process of a parallel platform according to claim 4, characterized in that, Impedance control based on Rotating Parallel Platform During the process, the X, Y, and E coordinates of the parallel platform are determined according to the TCP coordinate system {H} of the parallel platform. , Motion control quantity.

6. The method for shaft and spline mating during the flexible assembly process of a parallel platform according to claim 3, characterized in that, In step S35, the parallel platform coordinate system {P} is converted to the TCP coordinate system {H} to ensure that the movement of the bottom of the low-pressure vortex shaft is not large when the parallel platform rotates, thus avoiding collisions inside the compartment.

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