A vibration damping system for milling machining of an industrial robot and a milling vibration suppression method

Abstract

The present invention relates to the technical field of robot vibration damping, and solves the technical problems of poor vibration damping effect, low initiative and high limitation existing in the existing industrial robot vibration damping system. In particular, it relates to a vibration damping system for industrial robot milling and a milling vibration suppression method. The vibration damping system includes five piezoelectric ceramic stacks respectively distributed at the radial direction of the milling cutter tail and the axial end face of the milling cutter tail, which are used to suppress the vibration of the milling cutter in three directions of the three-dimensional space. The real-time dynamic milling force of the milling cutter tip point is measured by a laser vibrometer. The controller obtains the control force of the piezoelectric ceramic stack through analyzing the real-time dynamic milling force. The piezoelectric ceramic stack converts electrical energy into mechanical energy to actively control the vibration of the milling cutter shank and prevent the vibration from being transmitted to the robot body. The present invention adopts a full-active vibration control method, which has strong pertinence, the system responds to changes in a timely manner, can greatly improve the machining accuracy, is beneficial to improving the machining quality and stability of the robot, and has good universality.

Description

Technical Field

[0001] The present invention relates to the technical field of robot vibration damping, and particularly to a vibration damping system for industrial robot milling and a milling vibration suppression method. Background Art

[0002] The processing and assembly of complex components in aerospace require higher quality and precision, which puts forward higher requirements for the processing precision of industrial robots. With the emergence of high-end products such as the new generation of domestic large aircraft and large cabin spacecraft, due to the low stiffness of robots (usually only 1 / 50 of that of machine tools), they are prone to vibration under the action of cutting forces during processing, and the bottleneck effect of industrial robots in terms of processing precision becomes more and more obvious. In the field of high-end manufacturing, the demand for high-precision and high-performance processing robots is becoming increasingly urgent. How to reduce the vibration occurring during the processing of industrial robots has become a key problem that needs to be solved urgently.

[0003] In recent years, many scholars have begun to study the methods for suppressing robot processing vibration. The methods for suppressing processing vibration are divided into three categories: passive vibration suppression, semi-active vibration suppression, and active vibration suppression.

[0004] Chinese invention patent with publication number CN111390969A provides a vibration damping system and a robot having the same, which supplies electric energy to a piezoelectric vibration damping element to cause the piezoelectric vibration damping element to generate mechanical deformation so as to attenuate the vibration generated when a connection assembly operates. The reliability during the operation of the robot is increased, and the problem of power consumption is reduced. Although the above method reduces part of the vibration of the robot, it relies on the passive effect to deform the piezoelectric vibration damping element, and the vibration damping effect is not good.

[0005] Master's thesis of Hebei University of Technology, "Research on Vibration Suppression Method of Aerial Work Platform Based on Magnetorheological Damper", 2017 developed a set of semi-active vibration suppression system based on magnetorheological damper to suppress part of the working vibration of curtain wall installation robots.

[0006] Academic journal "IEEE International Conference on Robotics and Automation", 1998: 2476-2481 proposed an electrorheological fluid semi-active control damper to solve the problems of slow response and non-adjustable damping of general dampers. However, due to the instability and easy contamination of electrorheological fluid, it has no great practical value.

[0007] In semi-active control, without increasing energy consumption and system complexity, the response speed of the elastic element or damper of the system is slow, resulting in the system being unable to respond to changes in a timely manner, and the improvement of processing precision is limited. Therefore, the existing technology has limitations. Summary of the Invention

[0008] Aiming at the deficiencies of the prior art, the present invention provides a vibration damping system for industrial robot milling and a milling vibration suppression method, which solves the technical problems of poor vibration damping effect, low initiative and high limitation existing in the existing industrial robot vibration damping system.

[0009] To solve the above technical problems, the present invention provides the following technical solutions: A vibration damping system for industrial robot milling, including a robot body and a robot milling end effector connected thereto. The robot milling end effector is connected with a piezoelectric vibration damping tool holder through a tapered mandrel, and a milling cutter is detachably connected to the piezoelectric vibration damping tool holder;

[0010] The piezoelectric vibration damping tool holder is composed of a separable upper half of the tool holder and a lower half of the tool holder. The inside of the upper half of the tool holder is hollow for placing a piezoelectric ceramic stack. The piezoelectric ceramic stack consists of four radial piezoelectric ceramic stacks distributed in the radial planes at the tail of the milling cutter at 90° to each other in pairs, for suppressing the radial milling vibration force, and an axial piezoelectric ceramic stack distributed at the axial end face at the tail of the milling cutter, for suppressing the axial milling vibration force.

[0011] Further, on the radial plane at the tail of the milling cutter, the lower half of the tool holder is connected by a thread with a radial piezoelectric ceramic stack pre-tightening bolt providing a radial support plane for the radial piezoelectric ceramic stack. The radial piezoelectric ceramic stack acts on the radial direction of the tail of the milling cutter by means of the radial support plane;

[0012] On the axial end face at the tail of the milling cutter, the upper half of the tool holder is connected by a thread with an axial piezoelectric ceramic stack pre-tightening bolt providing an axial support plane for the axial piezoelectric ceramic stack. The axial piezoelectric ceramic stack acts on the axial direction of the tail of the milling cutter by means of the axial support plane.

[0013] Further, the outside of the piezoelectric vibration damping tool holder is connected with a brush slip ring through four tool holder and brush connection bolts. The inner ring of the brush slip ring is connected with the piezoelectric vibration damping tool holder by a bolt to rotate together. The outer ring of the brush slip ring is fixed by a bolt at the relatively stationary part of the robot milling end effector, serving as a sliding contact body for leading in and leading out current.

[0014] Further, an axial piezoelectric ceramic stack protection sleeve A and an axial piezoelectric ceramic stack protection sleeve B are connected to the axial piezoelectric ceramic stack by sintering. An axial piezoelectric ceramic stack support sleeve for stabilizing the axial piezoelectric ceramic stack, the axial piezoelectric ceramic stack protection sleeve A and the axial piezoelectric ceramic stack protection sleeve B is arranged inside the upper half of the tool holder.

[0015] Further, a radial piezoelectric ceramic stack protection sleeve A and a radial piezoelectric ceramic stack protection sleeve B are connected to the radial piezoelectric ceramic stack by sintering.

[0016] Further, a collet chuck and a lock nut for detachably mounting a milling cutter are provided on the lower half of the tool shank, and the milling cutter is clamped by the lock nut. The lock nut and the lower half of the tool shank are connected by a thread.

[0017] Further, the positioning surface of the milling cutter includes the cylindrical surface of the collet chuck and the lower bottom surface of the axial piezoelectric ceramic stack protection sleeve A.

[0018] Further, the damping system further includes:

[0019] A laser vibrometer for measuring the dynamic milling force of the tip point of the high-speed rotating milling cutter in real time by a non-contact method;

[0020] A controller, connected to the laser vibrometer and the piezoelectric ceramic stack power amplifier, adjusts the energization frequency and control voltage of the piezoelectric ceramic stack according to the dynamic milling force of the tip point, and outputs a control signal acting on the piezoelectric ceramic stack;

[0021] A piezoelectric ceramic stack power amplifier for power-amplifying the control signal and outputting it to the piezoelectric ceramic stack.

[0022] This technical solution also provides a milling vibration suppression method applied to the above damping system. The method includes the following steps:

[0023] S1. During milling, the laser vibrometer measures the vibration velocity of the laser measurement point on the cutter bar of the milling cutter in real time along the feeding direction of the industrial robot milling, and integrates the vibration velocity to obtain a vibration displacement signal;

[0024] S2. The controller receives the vibration displacement signal transmitted by the laser vibrometer, separates and eliminates the interference signal of the radial non-coincidence error and roundness error of the rotating tool, and obtains a continuous milling force signal according to the relationship between the milling cutter vibration displacement and the milling force;

[0025] S3. Calculate the dynamic milling force from the vibration displacement according to the static calibration of the measurement system, design a compensation link by the zero-pole placement method to dynamically compensate the measurement system, and perform dynamic error compensation of the milling force to obtain the real-time dynamic milling force of the tip point of the milling cutter;

[0026] S4. Use the LQR control algorithm to calculate the piezoelectric control force signal that the piezoelectric ceramic stack should output according to the real-time dynamic milling force of the tip point of the milling cutter;

[0027] S5. Output the piezoelectric control force signal to the piezoelectric ceramic stack power amplifier, and then control the piezoelectric ceramic stack to output a piezoelectric force for suppressing the vibration of the milling cutter.

[0028] With the above technical solutions, the present invention provides a vibration damping system for industrial robot milling and a milling vibration suppression method, which at least has the following beneficial effects:

[0029] 1. The piezoelectric vibration damping tool holder for robot milling provided by the present invention uses five piezoelectric ceramic stacks connected in parallel at the electrical level and in parallel at the mechanical level, which increases the energy conversion rate, reduces the vibration amplitude of the milling cutter shank from three-dimensional directions in the three-dimensional space, suppresses the milling force, and avoids transmitting the vibration to the robot body, thereby reducing the probability of robot chatter from the source and having a good vibration suppression effect.

[0030] 2. The piezoelectric vibration damping system for robot milling provided by the present invention uses a non-contact laser vibration measurement method to realize the real-time measurement of the dynamic milling force at the tip point of the milling cutter, dynamically compensates for the problem of distorted milling force measurement at high milling speeds of the milling cutter, improves the bandwidth of the measurement system, and provides a real and effective input signal for the subsequent vibration suppression of the milling cutter, with strong pertinence.

[0031] 3. The present invention embeds a vibration control algorithm in the controller, adjusts the energization frequency and control voltage of the piezoelectric ceramic stack according to the real-time dynamic milling force at the tip point of the milling cutter, makes it change in real time with the external excitation frequency of the industrial robot cutting process, and then realizes the vibration adaptive control of the industrial robot, further improving the machining quality and stability of the robot and having good universality. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The drawings described herein are used to provide a further understanding of the present application and form a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation of the present application. In the drawings:

[0033] Figure 1 It is a schematic diagram of the installation and connection between the devices of the vibration damping system of the present invention;

[0034] Figure 2 It is an internal sectional view of the piezoelectric vibration damping tool holder of the present invention;

[0035] Figure 3 It is a schematic diagram of the position of the piezoelectric ceramic stack inside the piezoelectric vibration damping tool holder of the present invention.

[0036] In the figure: 1. Robot body; 2. Robot milling end effector; 3. Piezoelectric vibration damping tool holder; 4. Workpiece; 5. Workbench; 6. Laser vibrometer; 7. Controller; 8. Piezoelectric ceramic stack power amplifier; 9. Upper half of the tool holder; 10. Brush slip ring; 11. Axial piezoelectric ceramic stack pre-tightening bolt; 12. Axial piezoelectric ceramic stack support sleeve; 13. Axial piezoelectric ceramic stack protective sleeve A; 14. Axial piezoelectric ceramic stack; 15. Axial piezoelectric ceramic stack protective sleeve B; 16. Radial piezoelectric ceramic stack pre-tightening bolt; 17. Radial piezoelectric ceramic stack protective sleeve A; 18. Radial piezoelectric ceramic stack; 19. Radial piezoelectric ceramic stack protective sleeve B; 20. Tool holder and brush connection bolt; 21. Lower half of the tool holder; 22. Collet chuck; 23. Milling cutter; 24. Locking nut. Detailed implementation manners

[0037] To make the above objects, features, and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific implementation manners. Thus, the implementation process of how this application uses technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly.

[0038] Industrial robots have many disadvantages during the machining process. For example, their structural stiffness is weak, the natural frequency is low, and the anti-interference ability is poor. When robots are applied in the aerospace manufacturing field and cutting difficult-to-machine materials such as titanium alloys and nickel-based alloys, significant cutting force disturbances will occur, which are extremely likely to cause cutting vibrations, affect the shape accuracy and surface quality of the machined parts, shorten the overall service life of the parts, and greatly limit the application process of industrial robots in the high-end manufacturing field. At the same time, the machining force acts on the robot body in reverse, resulting in structural fatigue of the industrial robot and shortening the service life of the robot. Especially when chatter occurs, the machining accuracy and quality are greatly reduced, and it is easy to cause damage to the robot and scrapping of high-value products. Therefore, how to suppress robot machining chatter and achieve high-precision and high-quality machining of robots is an urgent problem to be solved.

[0039] Based on the technical problem of vibration that occurs during the machining process of industrial robots, please refer to Figures 1 - 3, this embodiment proposes a vibration damping system for industrial robot milling. Five piezoelectric ceramic stacks are connected in parallel at the electrical level and in parallel at the mechanical level, increasing the energy conversion rate, reducing the vibration amplitude of the milling cutter shank in three-dimensional directions of the three-dimensional space, suppressing the milling force, avoiding the transmission of vibration to the robot body, and thus reducing the probability of robot chatter from the source, with good vibration suppression effect. There is a robot body 1 installed on the work station and a robot milling end effector 2 connected thereto. The robot milling end effector 2 is connected with a piezoelectric vibration damping tool holder 3 through a tapered mandrel. A milling cutter 23 is detachably connected to the piezoelectric vibration damping tool holder 3. The workpiece on the workbench 5 is milled by the milling cutter 23. The piezoelectric vibration damping tool holder 3 and the robot milling end effector 2 are connected by a pull stud. The robot milling end effector 2 is connected to the robot body 1 through a flange. The positioning surface of the milling cutter 23 includes the cylindrical surface of the spring collet 22 and the lower bottom surface of the axial piezoelectric ceramic stack protective sleeve A 15.

[0040] Among them, the laser vibrometer 6 measures the dynamic milling force of the tip point of the high-speed rotating milling cutter 23 in real time by a non-contact method; the controller 7 is connected to the laser vibrometer 6 and the piezoelectric ceramic stack power amplifier 8, adjusts the energization frequency and control voltage of the piezoelectric ceramic stack according to the dynamic milling force of the tip point, and outputs a control signal acting on the piezoelectric ceramic stack; the piezoelectric ceramic stack power amplifier 8 amplifies the power of the control signal and outputs it to the piezoelectric ceramic stack. The laser vibrometer 6, the controller 7, the piezoelectric ceramic stack power amplifier 8, the brush slip ring 10, and the piezoelectric vibration damping tool holder 3 are connected by signal lines. The laser vibrometer 6 measures the vibration displacement of the shank of the milling cutter 23 by non-contact vibration measurement means to realize the real-time measurement of the dynamic displacement signal of the tip point of the milling cutter during the machining process.

[0041] The piezoelectric vibration damping system for robot milling provided by this embodiment adopts a non-contact laser vibration measurement method to realize the real-time measurement of the dynamic milling force of the tip point of the milling cutter, dynamically compensates the problem of measurement distortion of the milling force under the high-speed milling speed of the milling cutter, improves the bandwidth of the measurement system, provides a real and effective input signal for the subsequent vibration suppression of the milling cutter, and has strong pertinence.

[0042] The piezoelectric vibration damping tool holder 3 is composed of a separable upper part 9 of the tool holder and a lower part 21 of the tool holder. The piezoelectric vibration damping tool holder 3 is manufactured in two parts, upper and lower. The upper part 9 of the tool holder is connected to the robot milling end effector 2 by a pull stud. The lower part 21 of the tool holder holds important components such as a spring collet 22, a milling cutter shank, and a locking nut 24. The interior of the upper part 9 of the tool holder is hollow to accommodate a piezoelectric ceramic stack. The piezoelectric ceramic stack consists of a radial piezoelectric ceramic stack 18 composed of four pairs distributed in the radial plane at 90° to each other at the tail of the milling cutter 23 to suppress the radial milling vibration force, and an axial piezoelectric ceramic stack 14 distributed at the axial end face at the tail of the milling cutter 23 to suppress the axial milling vibration force. Specifically, there are five piezoelectric ceramic stacks distributed inside the piezoelectric vibration damping tool holder. Four of them are distributed in the radial direction at 90° to each other at the tail of the milling cutter to suppress the radial milling vibration force, and the remaining one is distributed at the axial end face at the tail of the milling cutter to suppress the axial milling vibration force.

[0043] It should be further noted that piezoelectric ceramics have become an intelligent material that has developed extremely rapidly in recent years due to their advantages such as small volume, light weight, strong linear relationship between piezoelectric parameters, large stiffness, fast response speed, large output force, and wide frequency band. The piezoelectric ceramic stack is formed by stacking polycrystalline ceramics with piezoelectric effects through sintering. Electrodes are placed on the sides of each layer of polycrystalline ceramics, thus creating the actual effect of electrical parallel connection and mechanical series connection after the stacking of multiple layers of polycrystalline ceramics. After polarization treatment, the piezoelectric ceramic stack, under the inverse piezoelectric effect, converts electrical energy into mechanical energy in the polarization direction of the piezoelectric material.

[0044] Specifically, according to the first set of piezoelectric equations in the constitutive relationship of piezoelectric materials, after adopting equivalent mechanical stiffness and equivalent electrical stiffness, when restricting the degrees of freedom in the constrained expansion and contraction directions, it can be considered that the control voltage of the piezoelectric ceramic stack is proportional to the output piezoelectric force at both ends. The piezoelectric ceramic stack is used inside the piezoelectric vibration damping tool holder 3 to control the vibration of the shank of the milling cutter 23. Using the principle of electrical energy - mechanical energy conversion of piezoelectric ceramics, that is, the inverse piezoelectric effect, a voltage is applied to the electrodes at both ends of the piezoelectric ceramic. The piezoelectric ceramic undergoes relative displacement under the electric field force, generating a piezoelectric force and outputting it to the shank of the milling cutter 23 to suppress the vibration of the shank of the milling cutter 23.

[0045] Here, a piezoelectric ceramic stack with a single polarization direction is selected. In order to suppress the vibration generated by a milling force of about 200 N in robot milling, the technical parameters of the piezoelectric ceramic stack are shown in Table 1. Under the mechanical clamping at both ends of the piezoelectric ceramic stack, the output force of the piezoelectric ceramic stack is controlled by inputting a voltage to achieve targeted vibration control in robot milling. It should be noted that for a piezoelectric ceramic stack with determined basic parameters, its converted material parameters such as dielectric constant, piezoelectric elastic coefficient, and piezoelectric strain constant are also determined accordingly, and will not be elaborated here.

[0046] Table 1 Technical Parameters of Piezoelectric Ceramic Stack

[0047] Length × Width [mm2] Height [mm] Drive Voltage [V] Displacement [μm] Capacitance [nF] Stiffness [N / μm] Output [N] 5×5 4 150 3.3 180 318 1050

[0048] At the radial plane at the tail of the milling cutter 23, a radial piezoelectric ceramic stack pre-tightening bolt 16 that provides a radial support plane for the radial piezoelectric ceramic stack 18 is connected to the lower half 21 of the tool shank by a thread. The radial piezoelectric ceramic stack 18 acts on the radial direction of the tail of the milling cutter 23 by means of the radial support plane; at the axial end face at the tail of the milling cutter 23, an axial piezoelectric ceramic stack pre-tightening bolt 11 that provides an axial support plane for the axial piezoelectric ceramic stack 14 is connected to the upper half 9 of the tool shank by a thread. The axial piezoelectric ceramic stack 14 acts on the axial direction of the tail of the milling cutter 23 by means of the axial support plane.

[0049] It should be further noted that since each piezoelectric ceramic stack has a single output direction, in order to suppress the vibration of the milling cutter 23 tool bar in three-dimensional directions, five piezoelectric ceramic stacks that are mechanically and electrically parallel are selected in this embodiment to act on the end of the milling cutter inside the tool shank. Figure 2 It can be seen that there is an installation groove for placing the radial piezoelectric ceramic stack in the lower half 21 of the tool shank. The radial piezoelectric ceramic stack pre-tightening bolt 16 is connected to the lower half 21 of the tool shank by a thread to provide a support surface for the output of the radial piezoelectric ceramic stack 18. The radial piezoelectric ceramic stack protective sleeves A and B are connected to the radial piezoelectric ceramic stack 18 by sintering to avoid relative sliding so as to prevent tangential force from damaging the piezoelectric ceramic stack during the action. Through the action of the support surface, the radial piezoelectric ceramic stack 18 conducts the piezoelectric force to the end of the milling cutter 23, thereby suppressing the vibration generated by the milling force borne by the tip point of the milling cutter.

[0050] At the axial end face at the tail of the milling cutter, the axial piezoelectric ceramic stack pre-tightening bolt 11 is connected to the upper half 9 of the tool shank by a thread to provide a support plane for the axial piezoelectric ceramic stack 14. The axial piezoelectric ceramic stack 14 acts on the axial direction of the tail of the milling cutter 23 by means of the support plane. During rotation, due to the action of centrifugal force, the axial piezoelectric ceramic stack 14 and the axial piezoelectric ceramic stack protective sleeves A and B are easily thrown off. Therefore, another axial piezoelectric ceramic stack support sleeve 12 is designed to protect the axial piezoelectric ceramic stack and the protective sleeve, and the support sleeve is connected to the lower half of the tool shank by bolts.

[0051] The upper half 9 of the tool shank and the lower half 21 of the tool shank are connected by four high-strength M6 bolts axially. Thanks to the advantages of small size and large output of the piezoelectric ceramic stack, in order to achieve high rotational speed, further improve the machining quality and stability of the robot, and have good universality, the outer diameter of the tool shank is only 60 mm. The outside of the tool shank is connected to the brush slip ring 10 by four tool shank and brush connection bolts 20. The outer ring of the piezoelectric damping tool shank 3 is connected to the inner ring of the brush slip ring 10 by bolts, that is, the inner ring of the brush slip ring 10 rotates together with the piezoelectric damping tool shank 3. The inner ring of the brush slip ring 10 can extend the wire to supply power to the piezoelectric ceramic stack. The outer ring of the brush slip ring 10 is stationary and extends the external wire to connect to the external power supply. The motor brush is used on the commutator or slip ring of the motor as a sliding contact body for leading in and leading out current. Its main function is to conduct electricity while rubbing against metal.

[0052] The outside of the piezoelectric damping tool shank 3 is connected with a brush slip ring 10 by four tool shank and brush connection bolts 20. The inner ring of the brush slip ring 10 is connected to the piezoelectric damping tool shank 3 by bolts and rotates together. The outer ring of the brush slip ring 10 is fixed to the relatively stationary part of the robot milling end effector 2 by bolts. As a sliding contact body for leading in and leading out current, its main function is to conduct electricity while rubbing against metal. Specifically, the upper half 9 of the tool shank and the lower half 21 of the tool shank are connected by four high-strength bolts axially, and the four bolts are distributed in pairs at 90°.

[0053] Each piezoelectric ceramic stack has two protective sleeves that cooperate with the piezoelectric ceramic stack. The two protective sleeves are sintered together with the piezoelectric ceramic stack. The axial piezoelectric ceramic stack 14 is connected with an axial piezoelectric ceramic stack protective sleeve A 13 and an axial piezoelectric ceramic stack protective sleeve B 15 by sintering. The radial piezoelectric ceramic stack 18 is connected with a radial piezoelectric ceramic stack protective sleeve A 17 and a radial piezoelectric ceramic stack protective sleeve B 19 by sintering.

[0054] An axial piezoelectric ceramic stack support sleeve 12 for stabilizing the axial piezoelectric ceramic stack 14, the axial piezoelectric ceramic stack protective sleeve A 13, and the axial piezoelectric ceramic stack protective sleeve B 15 is arranged in the upper half 9 of the tool shank. During the rotation process, due to the action of centrifugal force, the axial piezoelectric ceramic stack 14 and the axial piezoelectric ceramic stack protective sleeves A and B are easily thrown off. Therefore, another support sleeve is designed to protect the axial piezoelectric ceramic stack and the protective sleeve, and the support sleeve is connected to the lower half of the tool shank by bolts.

[0055] A spring collet 22 and a locking nut 24 for detachably mounting a milling cutter 23 are provided on the lower half part 21 of the tool shank. The milling cutter 23 is clamped by the locking nut 24. The locking nut 24 and the lower half part 21 of the tool shank are connected by threads. The locking nut 24 and the spring collet 22 jointly perform mechanical positioning and clamping on the tool shank of the milling cutter 23. The head part of the milling cutter 23 is distributed with cutting edges and bears the milling force. The tail part of the milling cutter 23 bears the piezoelectric force, and the piezoelectric force reduces the cutting vibration by offsetting the milling force.

[0056] The piezoelectric vibration damping tool shank is distributed with five piezoelectric ceramic stacks, which are distributed at the radial direction of the tail part of the milling cutter and the axial end face of the tail part of the milling cutter to suppress the vibration in three directions of the three-dimensional space of the milling cutter. Through the non-contact vibration measurement method of laser vibration measurement, the real-time dynamic milling force of the tip point of the milling cutter is measured. The controller obtains the control force of the piezoelectric ceramic stack through analyzing the real-time dynamic milling force. The piezoelectric ceramic stack converts electrical energy into mechanical energy to actively control the vibration of the tool shank of the milling cutter and prevent the vibration from being transmitted to the robot body. The present invention adopts a full-active vibration control method, which has strong pertinence, the system responds to changes in a timely manner, can greatly improve the machining accuracy, is beneficial to improving the machining quality and stability of the robot and has good universality.

[0057] The piezoelectric vibration damping tool shank for robot milling provided in this embodiment adopts five piezoelectric ceramic stacks that are connected in parallel at the electrical level and in parallel at the mechanical level, increases the energy conversion rate, reduces the vibration amplitude of the tool shank of the milling cutter from the three-dimensional directions of the three-dimensional space, suppresses the milling force, avoids transmitting the vibration to the robot body, and thus reduces the probability of robot chatter from the source, and has a good vibration suppression effect.

[0058] This embodiment also proposes a milling vibration suppression method for use in conjunction with the vibration damping system for industrial robot milling. This method includes the following steps:

[0059] S1. During milling, a laser vibrometer measures the vibration velocity of the laser measurement point on the tool shank of the milling cutter in real time along the feed direction of the industrial robot milling, and obtains a vibration displacement signal after integrating the vibration velocity; specifically, the laser vibrometer measures the vibration of the milling cutter by the non-contact method of emitting laser. The laser vibrometer has high measurement resolution, is not sensitive to thermal error, and well solves the limitations of the existing dynamic milling force measurement methods in terms of the size, mass, measurement bandwidth, and installation method of the workpiece being machined. Therefore, during milling, the laser vibrometer measures the vibration velocity of the laser measurement point on the tool shank of the milling cutter in real time along the feed direction of the industrial robot milling, and a vibration displacement signal can be obtained after integrating the vibration velocity. It should be noted here that after measuring the vibration velocity of the tool shank of the milling cutter, the vibration displacement is obtained through frequency-domain integration. Frequency-domain integration can avoid the cumulative amplification effect of small errors during time-domain integration, and the displacement result is more accurate.

[0060] S2. The controller receives the vibration displacement signal transmitted by the laser vibrometer, separates the radial non - coincidence error and roundness error of the rotating tool to exclude interference signals, and obtains a continuous milling force signal based on the relationship between the vibration displacement of the milling cutter and the milling force. Specifically, the controller receives the dynamic vibration displacement signal transmitted by the laser vibrometer, first separates the radial non - coincidence error and roundness error of the rotating tool, excludes interference signals such as external cutting input, high - order harmonics of the motor, uneven air gap, and rotor mass imbalance, and obtains the milling force time - domain signal, that is, the continuous milling force signal, according to the relationship between the vibration displacement of the milling cutter and the milling force.

[0061] Specifically, after obtaining the continuous milling force signal, the corresponding output displacement of the piezoelectric ceramic stack is obtained through the LQR (Linear quadratic regulator) control algorithm, and the piezoelectric control force of the piezoelectric ceramic stack is calculated according to the equivalent mechanical stiffness and equivalent electrical stiffness of the piezoelectric ceramic stack to suppress the vibration of the milling cutter.

[0062] S3. Calculate the dynamic milling force from the vibration displacement according to the static calibration of the measurement system, design a compensation link through the zero - pole placement method to dynamically compensate the measurement system, and perform dynamic error compensation of the milling force to obtain the real - time dynamic milling force at the tip point of the milling cutter.

[0063] S4. Use the LQR control algorithm to calculate the piezoelectric control force signal that the piezoelectric ceramic stack should output according to the real - time dynamic milling force at the tip point of the milling cutter. After obtaining the real - time dynamic milling force at the tip point of the milling cutter, use the LQR control method to calculate the piezoelectric control force. LQR (Linear quadratic regulator) optimal control is based on full - state feedback control, with the integral of the weighted quadratic function of the state variable and the control input as the objective function, to find the optimal feedback gain matrix K with the lowest total cost, thus obtaining the desired control method, which belongs to the category of optimal control. It emphasizes obtaining the optimal dynamic performance within the complete time domain, controlling the variables of multiple - target performance through the cost function to obtain the optimal control law of the system state linear feedback. This method is easy to form a closed - loop optimal control, and the system can have good performance at low cost. The method is simple and easy to implement. The essence of LQR optimal control is to find an optimal solution that can consider both performance and input energy (meeting the control requirements with the minimum input value). The system performance index of LQR control is:

[0064] ;

[0065] Among them, Q matrix and R matrix are respectively the weight coefficient matrices of the state variable x and the control vector u The weight coefficient matrix Qor R The larger the element in R is, the greater the weight of the corresponding variable, and the more important it is in the performance function. The purpose of the optimal design of the LQR controller is to find a minimum system performance index J . Since variables with large weights will have a great impact on the system performance index, therefore, to require the minimum performance index means to minimize the variables with large weights, that is, the higher the constraints on the variables with larger weights. Here, after obtaining the real-time piezoelectric control force, the milling vibration of the milling cutter tip can be suppressed in real time.

[0066] S5. Calculate the piezoelectric control force signal that the piezoelectric ceramic stack should output according to the LQR control algorithm, and then output the piezoelectric control force signal to the piezoelectric ceramic power amplifier, and further control the piezoelectric ceramic stack to output the piezoelectric force to suppress the milling cutter vibration.

[0067] In this embodiment, through the vibration control algorithm embedded in the controller, the power-on frequency and control voltage of the piezoelectric ceramic stack are adjusted according to the real-time dynamic milling force of the milling cutter tip, so that it changes in real time with the external excitation frequency of the industrial robot cutting process, and further realizes the vibration adaptive control of the industrial robot, further improving the machining quality and stability of the robot and having good universality.

[0068] Those of ordinary skill in the art can understand that all or part of the steps in implementing the above embodiment methods can be completed by instructing relevant hardware through a program. Therefore, this application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, this application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0069] The above embodiments have introduced the present invention in detail. Specific examples are used in this article to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A vibration reduction system for industrial robot milling processing, comprising a robot body (1) and a robot milling end effector (2) connected thereto, characterized in that: The robot milling end effector (2) is connected to a piezoelectric vibration-damping tool holder (3) via a conical mandrel, and a milling cutter (23) is detachably connected to the piezoelectric vibration-damping tool holder (3); The piezoelectric vibration damping tool holder (3) is composed of a detachable tool holder upper part (9) and a tool holder lower part (21), and the interior of the tool holder upper part (9) is hollow for accommodating a piezoelectric ceramic stack, the piezoelectric ceramic stack comprising four radial piezoelectric ceramic stacks (18) distributed at 90 degrees in pairs on radial planes at the tail of the milling cutter (23) for suppressing radial milling vibration forces, and an axial piezoelectric ceramic stack (14) distributed at the axial end face of the tail of the milling cutter (23) for suppressing axial milling vibration forces; On a radial plane at the tail of the milling cutter (23), a radial piezoelectric ceramic stack pre-tightening bolt (16) is threadedly connected to the lower half of the shank (21) to provide a radial support plane for the radial piezoelectric ceramic stack (18), and the radial piezoelectric ceramic stack (18) applies piezoelectric force to the radial direction of the tail of the milling cutter (23) by means of the radial support plane; At the axial end face of the tail of the milling cutter (23), the upper half of the shank (9) is threadedly connected with an axial piezoelectric ceramic stack pre-tightening bolt (11) that provides an axial support plane for the axial piezoelectric ceramic stack (14). The axial piezoelectric ceramic stack (14) applies piezoelectric force to the axial direction of the tail of the milling cutter (23) by means of the axial support plane.

2. The vibration reduction system according to claim 1, characterized in that: The outside of the piezoelectric vibration damping tool holder (3) is connected to a brush slip ring (10) via four tool holder and brush connecting bolts (20); the inner ring of the brush slip ring (10) rotates together with the piezoelectric vibration damping tool holder (3) via a bolt connection; the outer ring of the brush slip ring (10) is fixed to a relatively stationary position of a robot milling end effector (2) via bolts, serving as a sliding contact body for conducting and introducing current.

3. The vibration reduction system according to claim 1, characterized in that: An axial piezoelectric ceramic stack protection sleeve A (13) and an axial piezoelectric ceramic stack protection sleeve B (15) are connected to the axial piezoelectric ceramic stack (14) by sintering, and an axial piezoelectric ceramic stack support sleeve (12) is provided in the upper part of the shank (9) for stabilizing the axial piezoelectric ceramic stack (14), the axial piezoelectric ceramic stack protection sleeve A (13) and the axial piezoelectric ceramic stack protection sleeve B (15).

4. The vibration reduction system according to claim 1, characterized in that: A radial piezoelectric ceramic stack protection sleeve A (17) and a radial piezoelectric ceramic stack protection sleeve B (19) are connected to the radial piezoelectric ceramic stack (18) by sintering.

5. The vibration reduction system according to claim 1, characterized in that: The lower part (21) of the tool handle is provided with a spring chuck (22) and a locking nut (24) for detachably mounting the milling cutter (23), and the milling cutter (23) is clamped by the locking nut (24), and the locking nut (24) and the lower part (21) of the tool handle are connected by threads.

6. The vibration reduction system according to claim 1, characterized in that: The positioning surface of the milling cutter (23) includes a cylindrical surface of the spring chuck (22) and a lower bottom surface of the axial piezoelectric ceramic stack protection sleeve B (15).

7. The vibration reduction system according to claim 1, characterized in that: The vibration reduction system further comprises: A laser vibrometer (6) for measuring the dynamic milling force of the tip of a high-speed rotating milling cutter (23) in real time by a non-contact method; A controller (7) connected to the laser vibrometer (6) and the piezoelectric ceramic stack power amplifier (8), adjusting the power-on frequency and control voltage of the piezoelectric ceramic stack according to the dynamic milling force of the tool tip, and outputting a control signal acting on the piezoelectric ceramic stack; The piezoelectric ceramic stack power amplifier (8) amplifies the power of the control signal and outputs it to the piezoelectric ceramic stack.

8. A milling vibration suppression method applied to the vibration reduction system according to any one of claims 1 to 7, characterized in that: The method comprises the following steps: S1. During milling, the laser vibrometer measures the vibration velocity of the laser measuring point of the milling cutter bar in real time along the feed direction of the industrial robot milling process, and obtains the vibration displacement signal after integrating the vibration velocity; S2, the controller receives the vibration displacement signal transmitted by the laser vibrometer, separates the radial misalignment error and roundness error of the rotating tool to eliminate the interference signal, and obtains the continuous milling force signal according to the relationship between the vibration displacement of the milling cutter and the milling force; S3, calculating the dynamic milling force from the vibration displacement according to the static calibration of the measurement system, and dynamically compensating the measurement system by designing the compensation link through the zero-pole configuration method, and performing dynamic error compensation of the milling force to obtain the real-time dynamic milling force of the tool tip of the milling cutter; S4, using the LQR control algorithm to calculate the piezoelectric control force signal that the piezoelectric ceramic stack should output according to the real-time dynamic milling force of the tool tip of the milling cutter; S5. Output the piezoelectric control force signal to the piezoelectric ceramic stack power amplifier, thereby controlling the piezoelectric ceramic stack to output a piezoelectric force for suppressing the vibration of the milling cutter.

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