A method for compensating synchronization error of large inertia moving beam of gantry machine tool considering communication delay

Abstract

The present invention discloses a method for compensating synchronization error of a large inertia moving beam of a gantry machine tool considering communication delay, which includes: establishing a moving beam motion control model considering communication delay; analyzing the influence of the delay link on the system stability; designing a communication disturbance observer; and compensating for the synchronization error caused by the communication delay. The present invention uses a communication disturbance observer to have a good compensation capability for the synchronization error caused by the communication delay of the moving beam numerical control system, and improves the system dynamic response performance, robustness and stability.

Description

Technical Field

[0001] The invention belongs to the technical field of numerical control machine tool control, and in particular relates to a method for compensating synchronous errors of a large-inertia moving beam of a gantry machine tool taking communication delay into consideration. Background Art

[0002] As the core of "industrial mother machine", the structure and control accuracy of high-end CNC machine tools are the key links that affect their processing accuracy. Research on the common key technologies of high-end CNC machine tools plays an important role in promoting the development of my country's manufacturing industry. As a common high-end CNC machine tool, the beam structure of the moving beam gantry machining center is supported by double columns, and the beam is driven by dual motors to move to complete the heavy cutting of large mass, large volume and irregularly shaped parts. For example, key parts of large submarines and large ships at sea. It can be seen that the gantry machining center is an important strategic resource of the country and a display of the strength of a country's military industry and large heavy industry. The structural advantage of the moving beam gantry machining center is that it can enable the machine tool to obtain higher structural rigidity and control bandwidth. However, the moving beam has the characteristics of large inertia and high-speed movement, which makes it difficult to ensure the synchronous drive accuracy of the moving beam, and at the same time affects the processing accuracy. Therefore, it is of great significance to study the synchronous drive strategy when the beam moves.

[0003] At present, most of the existing control methods for synchronous drive of the moving beam of the gantry machining center adopt a structure in which the CNC system is responsible for calculation and the servo drive is responsible for execution, and is controlled through a three-closed loop (position loop, speed loop, current loop) structure. The servo drive is controlled by the speed loop and the current loop, and the CNC system executes the control instructions of the position loop. The CNC system exchanges data with the two servo axes driving the crossbeam through bus communication. Its working process is as follows: the servo drives on both sides of the crossbeam feed back the position signal to the CNC system through bus communication; the CNC system then transmits the speed command to the servo drives on both sides of the crossbeam through bus communication, and completes the synchronous drive of the crossbeam. However, in the process of bus communication between the CNC system and the servo drive, it is inevitable that there will be a time delay link in the position loop control loop. The existence of communication delay will reduce the gain margin of the position loop and destroy the stability of the system. It will increase the synchronization error when the crossbeam moves and reduce the machining accuracy of the gantry machine tool.

[0004] The essence of communication delay is that the time delay link is introduced into the position loop in the servo control system, which reduces the gain margin of the position loop. In order to reduce the delay of this link, the commonly used methods are divided into hardware methods and software methods:

[0005] (1) Hardware method: Reduce the delay link by adopting new hardware design. For example, use high-precision grating scales and encoders, use communication methods with higher transmission frequencies, and use control chips with better performance. Existing literature: Wang Bangji, Wang Dong, Xu Rui, Zhang Wenxuan, Liu Qingxiang. Application of MPSoC in multi-axis servo motor drivers [J]. Journal of Electric Machines and Control, 2021, 25(12): 19-26. In view of the problem that a single chip is difficult to achieve independent and synchronous drive control of multi-axis servo motors, a multi-axis servo motor drive control scheme based on a multi-processor system-on-chip is proposed. This technology can solve the problem that a single chip is difficult to achieve independent and synchronous drive control of multi-axis servo motors, while minimizing the impact of communication delay on servo performance.

[0006] (2) Software method: Under the condition that the hardware conditions of the servo system remain unchanged, different algorithms are designed to reduce the impact of communication delay on the performance of the control system. Existing literature: Khanesar MA, Kaynak O, Yin Shen, et al. Adaptive indirect fuzzy sliding mode controller for networked control systems subject to time-varying network induced time delay[J]. IEEE Transactions on Fuzzy Systems, 2014, 23(1): 205-214. A new fuzzy sliding mode controller is adopted to control the nonlinear dynamic system on the network, which is affected by bounded external disturbances, communication delays caused by time-varying networks and packet loss; Existing literature: Natori K, Tsuji T, Ohnishi K, et al. Time-delay compensation by communication disturbance observer for bilateral teleoperation under time-varying delay[J]. IEEE Transactions on Industrial Electronics, 2010, 57(3): 1050-1062. A communication delay compensation method based on network disturbance and communication disturbance observer is introduced and the effectiveness of this method in compensating operating system errors under time-varying communication delay is verified.

[0007] The essence of communication delay is that a time delay link is introduced into the position loop in the servo control system, which reduces the gain margin of the position loop. In order to reduce the delay of this link, the commonly used methods are divided into hardware methods and software methods, but both have different disadvantages in the existing technology:

[0008] (1) Hardware: The high-speed and high-precision processing requirements of high-end CNC machine tools have extremely high requirements for position gain margin. If you want to reduce the synchronization error of the moving beam caused by communication delay in hardware, you need to optimize the hardware facilities during the design and manufacturing process of the machine tool. Even if you use a higher-precision grating scale and encoder, a communication method with a higher transmission frequency, or a control chip with better performance, all three methods can reduce the synchronization error of the moving beam, but the improvement of the accuracy of the hardware facilities will increase the manufacturing cost, and the synchronization error of the moving beam can only be measured after the machine tool is manufactured, and the effectiveness of each method cannot be verified through simulation experiments. Therefore, there is an urgent need for a hardware control device that uses a communication protocol to connect to the outside of the machine tool to solve the defects of the above methods and meet the needs of reducing the delay link.

[0009] (2) Software: There are several main methods to reduce latency through software, but they all have different disadvantages.

[0010] ① Smith prediction compensation method: Before using this method, you need to know the accurate system model, then predict the system with time delay, and finally compensate the error term to the servo controller as an input. The accuracy of Smith prediction compensation method depends on the system model. When there is an error in the system model, the compensation effect will be significantly worse.

[0011] ② Fuzzy control, neural network control and expert control, etc.: Although these algorithms can compensate for communication delays while taking into account the robustness of the servo system, their disadvantages are also obvious. For example, fuzzy control is not suitable for high-precision control; neural network control requires more training sets and takes a long time to train; expert control relies too much on experience and knowledge and lacks self-learning ability. Therefore, the above control methods are difficult to apply to machine tool servo systems.

[0012] In view of the defects in the existing technology, the purpose of the present invention is to design a communication disturbance observer that can compensate for the synchronization error of the moving beam of the moving beam gantry machining center caused by communication delay, so as to meet the application requirements of high-precision synchronization control of the crossbeam of the moving beam gantry machining center. Summary of the invention

[0013] In view of this, the technical problem to be solved by the present invention is to provide a method for compensating the synchronization error of a large-inertia moving beam of a gantry machine tool taking into account the communication delay. By using a communication interference observer, the synchronization error of the moving beam caused by the communication delay of the numerical control system can be well compensated, and the dynamic response performance, robustness and stability of the system can be improved.

[0014] In order to solve the above technical problems, the present invention discloses a method for compensating synchronization error of a large inertia moving beam of a gantry machine tool considering communication delay, which comprises:

[0015] Step 1. Establish a moving beam motion control model considering communication delay;

[0016] Step 2. Analyze the impact of the delay link on system stability;

[0017] Step 3. Design a communication disturbance observer;

[0018] Step 4. Compensate for the synchronization error caused by communication delay.

[0019] According to one embodiment of the present invention, the above-mentioned moving beam motion control model is based on the three-closed-loop control structure of the gantry machine tool, and the three-closed-loop control structure of the gantry machine tool consists of three parts: a numerical control device, a servo drive device, and a mechanical structure; the position loop is executed in the numerical control device, and the servo drive device is controlled by a current loop and a speed loop. The numerical control device exchanges data with each servo axis through bus communication to complete the synchronous drive of the moving beam.

[0020] According to one embodiment of the present invention, the control model is ; Where t1 and t2 represent the time delay in the forward path and the reverse path respectively, G p (s) represents the transfer function of the position loop, G a (s) represents the transfer function including the velocity loop and the mechanical model; its expression is: Where K T is the motor torque constant, divided by K T Other parameters have been mentioned above and will not be repeated here;

[0021] Combined with G p (s) and G a (s) The characteristic equation of the system is: The open-loop transfer function of the system is: Delay link Approximately the first-order Pade link to ensure the accuracy of the amplitude, the first-order Pade link formula is as follows: According to one embodiment of the present invention, the communication disturbance observer (CDOB) compensates for the communication delay link of the numerical control system by treating the delay link as the disturbance of the system; the disturbance principle is: ;in, is the time delay link, T is the time delay period; is the disturbance term, and its expression is: Delay Link It can be approximated by a first-order Pade link: The extreme points of this expression are (Pole of the disturbance term); the CDOB low-pass filter form is: Where: f c is the cutoff frequency of the low-pass filter; the pole of this expression is p codb =-f c (The pole of the CDOB low-pass filter). According to an embodiment of the present invention, the design criterion of the CDOB is: The transient response of the CDOB is faster than the transient response of the disturbance term; the design criterion can be expressed as: Substitute p dis and p codb The expression of can be obtained as follows:

[0022] According to an embodiment of the present invention, in actual applications, the pole positions of the designed CDOB need to be selected according to the system response under actual working conditions. When the CDOB is stable, different pole positions will result in different system responses.

[0023] According to one embodiment of the present invention, in the above step four, an open control system of BECKHOFF company is used, and the TE1400 engineering module in the built-in control software TwinCAT compiles the MATLAB / Simulink model into a TcCOM module with an I / O interface, which is imported into the running core in TwinCAT for execution; at the same time, a virtual axis is created to receive the position command of the numerical control system and make the movable beam move under ideal conditions; two moving axes are created and connected to the actual motor shaft, and the two axes obtain the synchronous error compensation correction value added to the two ends of the moving axis through the CDOB constructed by the present invention, and are connected to the position command of the virtual axis, and the two axes are controlled respectively after the final corrected actual position command of the Z1 axis and the Z2 axis is obtained through cross-coupling control, so as to realize the synchronous error compensation of the synchronous drive system of the gantry movable beam.

[0024] Compared with the prior art, the present invention can achieve the following technical effects:

[0025] The present invention has practical significance in the actual application of task offloading of computing tasks generated by network physical machine tools in the framework of intelligent CNC systems. It not only effectively reduces the delay of task offloading, but also improves the utilization efficiency of computing resources in intelligent CNC workshops and improves the accuracy of digital twin models.

[0026] Of course, any product implementing the present invention does not necessarily need to achieve all of the above-mentioned technical effects at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0028] Figure 1 It is the overall flow chart of the present invention;

[0029] Figure 2 This is the Smith predictive compensator principle of the present invention;

[0030] Figure 3 It is the structural diagram of the beam synchronous drive system;

[0031] Figure 4 It is a schematic diagram of the three-closed-loop control structure of the gantry machine tool;

[0032] Figure 5 It is the block diagram of the crossbeam synchronous drive control system of the gantry machine tool including communication delay;

[0033] Figure 6 It is a simplified control system block diagram of the beam synchronous drive of the gantry machine tool including communication delay;

[0034] Figure 7 It is the root locus diagram of the control system during different time delays;

[0035] Figure 8 It is the schematic diagram of network disturbance estimation;

[0036] Fig. 9 This is the principle diagram of using CDOB for delay compensation;

[0037] Fig.10 It is a schematic diagram of the beam motion curve under different methods. DETAILED DESCRIPTION

[0038] The following will describe the implementation methods of the present invention in detail with reference to the accompanying drawings and embodiments, so that the implementation process of how the present invention applies technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly.

[0039] Please refer to Figure 1The present invention discloses a method for compensating synchronization error of a large inertia moving beam of a gantry machine tool considering communication delay, which comprises:

[0040] Step 1. Establish a moving beam motion control model considering communication delay;

[0041] Step 2. Analyze the impact of the delay link on system stability;

[0042] Step 3. Design a communication disturbance observer;

[0043] Step 4. Compensate for the synchronization error caused by communication delay.

[0044] 1. Establish a moving beam motion control model considering communication delay

[0045] The three parts of the gantry machine tool are the three-closed-loop control structure of the numerical control device, the servo drive device, and the mechanical structure. The position loop is executed in the numerical control device, the servo drive device is controlled by the current loop and the speed loop, and the numerical control device exchanges data with each servo axis through bus communication to complete the synchronous drive of the moving beam. Combined with the way in which the moving beam of the gantry machine tool generates communication delay during movement, a moving beam motion control model that takes into account the communication delay can be obtained.

[0046] 2. Analyze the impact of delay on system stability

[0047] After simplifying the control system model in step 1, the closed-loop transfer function of the system is calculated to obtain the characteristic equation and open-loop transfer function of the system. First, the characteristics of the characteristic equation of the system are analyzed, and then the poles and zeros of the open-loop transfer function are studied by the root locus method to determine the changing trend of the roots (poles) of the characteristic equation of the closed-loop transfer function with the gain of the position loop controller. Finally, the influence of the delay link on the stability of the system is analyzed, and the necessity of delay compensation is pointed out.

[0048] 3. Design of communication disturbance observer

[0049] Although the Smith predictor compensator is often used in system compensation with time delay links, its principle Figure 2 As shown. Among them: are the controller transfer function, system transfer function and estimated model transfer function respectively, t p Estimated time delay.

[0050] For the above parameters: for large inertia components such as the gantry machine tool crossbeam, there will be a model mismatch problem. Secondly, the amount of data transmitted through the bus is different, and the specific communication delay time is difficult to obtain. Therefore, the Smith predictor compensator has poor robustness and is not suitable for the synchronous drive of the large inertia crossbeam of the gantry machine tool. In response to the above problems, the present invention uses a communication disturbance observer (CDOB) to equate the delay link to the disturbance of the system to compensate for the communication delay link of the numerical control system.

[0051] 4. Compensate for synchronization errors caused by communication delays

[0052] To obtain an ideal error compensation effect, the transient response of CDOB needs to be faster than the transient response of the disturbance term, that is, the pole configuration needs to satisfy the pole position of CDOB to be farther than the pole of the equivalent link of the delay link in order to obtain a better compensation effect. In practical applications, the pole position of the designed CDOB needs to be selected according to the system response under actual working conditions. When CDOB is stable, the system response obtained at different pole positions is different. In order to verify the effectiveness of CDOB, it is applied to the synchronous drive of the moving beam of the gantry machine tool to observe the compensation effect of CDOB on the synchronization error caused by communication delay under different working conditions.

[0053] 1.1 Structure diagram of beam synchronous drive system

[0054] Modern CNC systems use high-performance CPUs with strong computing and analysis capabilities and fast data feedback speeds. CNC systems represented by the foreign Siemens 828D and the domestic Huazhong CNC series usually use CNC systems to control servo drives to drive mechanical structure movements. That is, the CNC system is responsible for calculations, and the servo drive is responsible for execution. The position loop is executed in the CNC system, and the speed loop and current loop are executed in the servo drive. Its internal working process is as follows: the CNC system exchanges data with each servo axis through bus communication, and the servo drive of each axis feeds back the position signal to the CNC system through bus communication. Finally, the CNC system transmits the command signal to each servo drive through bus communication. The above process can complete the three-loop control of the position loop, speed loop, and current loop. Its structure diagram is as follows Figure 3 shown.

[0055] 1.2 Block diagram of the crossbeam synchronous drive control system including communication delay

[0056] Depend on Figure 4It can be seen that the movement process of the gantry machine tool moving beam is as follows: the servo motor shaft is connected to the ball screw. During the movement, the servo driver outputs an alternating current signal to the servo motor, and the motor shafts on both sides start to rotate to drive the ball screws, and the ball screws on both sides convert their rotational motion into the linear motion of the beam. Because the drive structure on both sides of the beam is the same, only the single-side drive structure is modeled and analyzed in the following analysis process.

[0057] The servo control system consists of three series loops: position loop, speed loop, and current loop. In the position loop, the position command is generated by the interpolator of the CNC system, and the position feedback is the position of one side of the moving beam, which can be directly measured by the linear grating ruler. Therefore, the position loop controller uses a P controller, and its proportional gain coefficient is K. p The speed command of the speed loop is the product of the position following error and the proportional gain. The speed feedback is the instantaneous speed of the motor output shaft, which is obtained by the encoder signal difference. Therefore, the speed loop adopts the PI controller K vi / s+K vp . Where K vi and K vp Respectively represent the gain coefficients of the integral link and the proportional link of the PI controller. For the processing of the current loop, the inner loop bandwidth of the control loop is too different from the outer loop bandwidth, so the current loop can be equivalent to a first-order inertia link. However, the present invention mainly analyzes the control error with the position loop, so the current loop is equivalent to unit 1.

[0058] From Section 1.1, we can know that the control structure based on bus communication will inevitably have communication delay in the position loop control loop, and the time delay is usually in the millisecond level, which cannot be ignored for the moving beam of the gantry machining center that pursues high-precision and high-response performance control. Therefore, it is necessary to consider the delay link of the position loop. Combining the relationship between the three-loop control of the servo control system, the mechanical structure of the moving beam, and the way the position loop of the CNC system generates communication delay, we can get the block diagram of the beam synchronous drive control system with communication delay as shown below. Figure 5 shown.

[0059] in: represents the delay link; J m , J1 are the motor inertia and the moving beam inertia respectively; K s It is the stiffness coefficient of flexible links such as screws.

[0060] 2. Analyze the impact of delay on system stability

[0061] 2.1 Model simplification

[0062] To facilitate analysis, the control system block diagram in step 1 is simplified ( Figure 5 ), and we get Figure 6 The control model shown.

[0063] Among them, t1 and t2 represent the time delay in the forward path and the reverse path respectively, G p (s) represents the transfer function of the position loop, G a (s) represents the transfer function including the speed loop and the mechanical model. Its expression is: Where K T is the motor torque constant, divided by K T Other parameters have been mentioned above and will not be repeated here. p (s) and G a (s) The characteristic equation of the system is: Combined with G p (s) and G a (s) The characteristic equation of the system is: Delay link Approximately the first-order Pade link to ensure the accuracy of the amplitude, the first-order Pade link formula is as follows: The root loci are shown in Figure 1 under the conditions of 1ms, 2ms, and 3ms delays. Figure 7 As shown in the figure is the position loop gain corresponding to the root locus.

[0064] Depend on Figure 7 From the root locus diagram, we can see that the time delay will affect the stability of the servo system. Specifically, the longer the time delay, the smaller the stability domain of the system and the smaller the position loop gain coefficient. Therefore, the existence of the time delay link will lead to a decrease in the position loop gain and limit the position loop bandwidth. Therefore, it is necessary to compensate for the error caused by the time delay link.

[0065] 3. Design of communication interference observer

[0066] For large inertia components such as the gantry machine tool crossbeam, the use of the Smith predictor compensator will have the problem of model mismatch, which reduces the stability of the servo system. Secondly, the amount of data transmitted through the bus is different, and the specific communication delay time is difficult to obtain. Therefore, the Smith predictor compensator has poor robustness and is not suitable for the synchronous drive of the large inertia crossbeam of the gantry machine tool. In response to the above problems, the present invention uses a communication disturbance observer (CDOB) to compensate for the communication delay link of the numerical control system by equating the delay link to the disturbance of the system.

[0067] The principle of CDOB is to compensate the system based on observing network disturbances. In fact, a system with a time delay link can be equivalent to a network disturbance system. Figure 8 Schematic diagram for network perturbation estimation; Fig. 9 The schematic diagram of delay compensation using CDOB is shown below. The design of CDOB is based on this schematic diagram.

[0068] in: is the time delay link, T is the time delay period; is the disturbance term, and its expression is: The delay link mentioned above It can be approximated by a first-order Pade link: It can be approximated by a first-order Pade link: (the pole of the disturbance term).

[0069] The design of the low-pass filter in CDOB affects the actual performance of CDOB. Assume that the low-pass filter of CDOB is in the form of: Where: f c is the cutoff frequency of the low-pass filter. The pole of this expression is p codb =-f c (The pole of the CDOB low-pass filter).

[0070] The design criteria of CDOB are: The transient response of CDOB is faster than the transient response of disturbance term. According to the control principle pole configuration principle, it can be known that the pole position of CDOB needs to be farther than the pole of the equivalent link of the delay link. At the same time, the stability criterion of Lyapunov system should be met. The above design criteria can be expressed as: Substitute p dis and p codb The expression of can be obtained as follows: In practical applications, the pole positions of the designed CDOB need to be selected according to the system response under actual working conditions. When the CDOB is stable, different pole positions will result in different system responses.

[0071] 4. Compensate for synchronization errors caused by communication delays

[0072] In order to verify the effectiveness of CDOB, it is applied to the synchronous drive of the moving beam of the gantry machine tool to observe its compensation effect on the synchronization error caused by communication delay.

[0073] Adopting the open control system of BECKHOFF, the TE1400 engineering module in the built-in control software TwinCAT compiles the MATLAB / Simulink model into a TcCOM module with an I / O interface, and imports it into the running core in TwinCAT for execution. At the same time, a virtual axis is created to receive the position command of the numerical control system and make the moving beam move under ideal conditions; two moving axes are created and connected to the actual motor axis, and the two axes obtain the synchronous error compensation correction value added to the two ends of the moving axis through the CDOB constructed by the present invention, and are connected to the position command of the virtual axis. After the cross-coupling control, the actual position command of the Z1 axis and the Z2 axis is obtained, and the two axes are controlled respectively to realize the synchronous error compensation of the gantry moving beam synchronous drive system.

[0074] The test results show that Fig.10 , if the position command of the beam is set to move 20mm, if the command is completed only by the function of the CNC system, the system response time is 0.04ms; the maximum synchronization error is about 0.3mm. When CDOB compensation is used, the system response time is 0.03ms; the maximum synchronization error is only 0.15mm, which is only half the size of the command completed by the function of the CNC system. The above results show that the interference suppression performance and dynamic response performance of the beam synchronization control have been significantly improved after adding the CDOB observer.

[0075] In summary, the present invention has practical significance in its actual application in the synchronous drive control of the crossbeam of a large moving beam gantry machining center. The verified test results of this control method show that the use of a communication interference observer can have a good compensation capability for the synchronization error of the moving beam caused by the communication delay of the numerical control system, and improve the dynamic response performance, robustness and stability of the system.

[0076] The above description shows and describes several preferred embodiments of the present invention, but as mentioned above, it should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the invention concept described herein through the above teachings or the technology or knowledge of the relevant field. Changes and variations made by those skilled in the art do not depart from the spirit and scope of the present invention, and should be within the scope of protection of the claims attached to the present invention.

Claims

1. A method for compensating synchronization error of a large inertia moving beam of a gantry machine tool considering communication delay, characterized in that: include: Step 1. Establish a moving beam motion control model considering communication delay; Step 2. Analyze the impact of the delay link on system stability; Step 3. Design a communication disturbance observer; Step 4. Compensate for the synchronization error caused by the communication delay; The moving beam motion control model is based on the three-closed-loop control structure of the gantry machine tool, which consists of a numerical control device, a servo drive device, and a mechanical structure. The position loop is executed in the CNC device, and the servo drive device is controlled by the current loop and the speed loop. The CNC device exchanges data with each servo axis through bus communication to complete the synchronous drive of the moving beam. Among them, t1 and t2 represent the time delay in the forward path and the reverse path respectively, G p (s) represents the transfer function of the position loop, G a (s) represents the transfer function including the velocity loop and the mechanical model; Indicates the delay link; Its expression is: G p (s)=K p(1) The position loop controller uses a P controller, and its proportional gain coefficient is K p The speed command of the speed loop is the product of the position following error and the proportional gain. The speed feedback is the instantaneous speed of the motor output shaft, which is obtained by the encoder signal difference. Therefore, the speed loop adopts the PI controller K vi / s+K vp ; where K vi and K vp Respectively represent the gain coefficients of the integral link and the proportional link of the PI controller, K T is the motor torque constant; J m , J1 are the motor inertia and the moving beam inertia respectively; K s is the stiffness coefficient of flexible links such as screws; Combined with G p (s) and G a (s) The characteristic equation of the system is: The open-loop transfer function of the system is: Delay link Approximately the first-order Pade link to ensure the accuracy of the amplitude, the first-order Pade link formula is as follows:

2. The method for compensating synchronization error of a gantry machine tool large inertia moving beam considering communication delay according to claim 1 is characterized in that: The communication disturbance observer CDOB equates the delay link to the disturbance of the system to compensate for the communication delay link of the numerical control system; Among them, e -Ts is the delay link, T is the time delay; D net (s) is the disturbance term, and its expression is: D net (s)=U(s)(1-e -Ts ) (6) Delay link -Ts It can be approximated by a first-order Pade link: The extreme points of this expression are In addition, the poles of the disturbance term; The CDOB low-pass filter is of the form: Where: f c is the cutoff frequency of the low-pass filter; the pole of this expression is p cdob =-f c , which is the pole of the CDOB low-pass filter.

3. The method for compensating synchronous error of a gantry machine tool large inertia moving beam considering communication delay according to claim 2 is characterized in that: The transient response of CDOB is faster than that of disturbance term. According to the control principle pole configuration principle, it can be known that the pole position of CDOB should be farther than the pole of the equivalent link of the delay link. At the same time, the Lyapunov system stability criterion should be met. The above design criteria can be expressed as: Rep cdob ]<Re[p dis ]<0 (9) Will and p cdob =-f c Substituting the expression into , we can get the pole configuration principle as follows: 。 4. The method for compensating synchronization error of a large inertia moving beam of a gantry machine tool considering communication delay according to claim 3 is characterized in that: In practical applications, the pole positions of the designed CDOB need to be selected according to the system response under actual working conditions. When the CDOB is stable, different pole positions will result in different system responses.

5. The method for compensating synchronization error of a large inertia moving beam of a gantry machine tool considering communication delay according to claim 4 is characterized in that: In the step 4, an open control system of BECKHOFF is used, and the TE1400 engineering module in the built-in control software TwinCAT compiles the MATLAB / Simulink model into a TcCOM module with an I / O interface, which is imported into the running core of TwinCAT for execution; at the same time, a virtual axis is created to receive the position command of the CNC system and make the movable beam move under ideal conditions; two moving axes are created and connected to the actual motor axis, and the two axes obtain the synchronous error compensation correction value through the constructed CDOB and add it to both ends of the moving axis, and are connected to the position command of the virtual axis, and the actual position commands of the Z1 axis and the Z2 axis are obtained after the final correction through cross-coupling control, and the two axes are controlled respectively to realize the synchronous error compensation of the gantry movable beam synchronous drive system.

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