Cross-coupled Control Research Articles

ILC-adapted parameter optimization of cross-coupled single-input fuzzy tracking controllers for an X-Y positioning table

ABSTRACT This article systematically formulates an optimized cross-coupled single-input fuzzy-logic control mechanism that aims to enhance the tracking and contouring control performance of an X-Y positioning table. The motion along each axis is controlled via dedicated tracking controllers. The ubiquitous Iterative-Learning-Controller (ILC) is a standard tracking controller commonly used for high precision dual-axis systems. However, it puts recursive computational burden on the computer and its performance deteriorates under abrupt parametric variations. Conversely, a well-postulated proportional-derivative type single-input fuzzy-logic controller is robust. It offers faster transient recovery against disturbances, computational efficiency, and minimal tracking error in the response. In this article, the least-squared-regression-method is used to adaptively adjust the shapes of fuzzy membership-functions according to the control trajectory generated by ILC. This synergistic collaboration enables the fuzzy controller to effectively reject any external bounded disturbances in plant dynamics, while adapting to the convergence and precise tracking control behavior of ILC. The motion control system is also augmented with a single-input fuzzy cross-coupling controller that improves the contouring accuracy of the drive system by effectively attenuating the effects of axis mismatch. The efficacy of the proposed controller is validated via hardware-in-the-loop experiments, by plotting a circular contour using an X-Y position table.

Real-time exact contour error calculation of NURBS tool path for contour control

The requirement of high-speed and high-precision contouring with NURBS tool path to the CNC machining process is increasing. The calculation of the contouring error (CE) of the NURBS tool path to real time is necessary for the advanced contour control like the cross-coupled controller (CCC). Based on the complexity of the CE calculation of NURBS, most studies use estimating methods to approximate the real CE in the controller. However, when the cutter is at the large curvature zones in the high-speed machining, the difference between the estimated the CE and the real one becomes large. To solve this problem, an algorithm to calculate the exact CE of NURBS tool path to real time is proposed. The calculation model of the CE of NURBS is derived. Also, the numerical calculation algorithm from Brent’s method is given to solve the CE model. Multiple solutions of CE model is discussed and real-time solution tracking method is developed to determine the intervals of the candidate solutions for numerical calculation. Contour error for control (CCE) is proposed for controller design to improve the stability of contour control, which is different from the definition of conventional control error for measurement (MCE). The proposed algorithm is validated for both the simulation and the experiment on the X–Y table. Experimental results show the effectiveness of the proposed algorithm and the actual CE is reduced significantly compared with other methods.

Adaptive Model-Free Coupling Controller Design for Multi-Axis Motion Systems

In this study, we introduce an adaptive model-free coupling controller while using recurrent fuzzy neural network (RFNN) for multi-axis system to minimize the contour error. The proposed method can be applied to linear or nonlinear multi-axis motion control systems following desired paths. By the concept of cross-coupling control (CCC), multi-axis system is transferred into a nonlinear time-varying system due to the time-dependent coordinate transformation; tangential, normal, and bi-normal components of desired contour. Herein, we propose a model-free adaptive coupling controller design approach for multi-axis linear motor system with uncertainty and nonlinear phenomena. RFNN establishes the corresponding adaptive coupling controller to treat the uncertain system with nonlinear phenomenon. The stability of closed-loop system is guaranteed by the Lyapunov method and the adaptation of RFNN is also obtained. Simulation results are introduced in order to illustrate the effectiveness.

Definition and estimation of joint-space contour error based on generalized curve for five-axis contour following control

Five-axis contour following is one of the main tasks for five-axis CNC machine tools. The contour following accuracy directly determines the final machining precision. Therefore, control of the five-axis contour error is significant. Currently, most existing definitions of five-axis contour error are in the Cartesian task space, and this inevitably requires direct and inverse Jacobian transformations between the task-space contour-error computation and the joint-space contour-error control. Different from them, this paper defines the five-axis contour error in the ℝ5 joint space through adjusting uniform units of five joints, and accordingly proposes a third-order estimation algorithm for the defined joint-space contour error, with the help of the concept of generalized curve. Based on the joint-space contour-error definition and estimation, a joint-space five-axis cross-coupling control scheme is finally provided. Simulation and experimental results demonstrate that the presented third-order joint-space contour-error estimation algorithm has a satisfactory estimation accuracy, and the presented joint-space five-axis contour control method can decrease both of the joint-space and the task-space five-axis contour errors by more than 49%. It is also analyzed and verified that comparing with routine task-space five-axis contour control method, the presented joint-space method not only needs not the direct and inverse Jacobian transformations during error estimation, which saves the computational burden, but also generates minimum axial contour-control commands, which enhances the control stability, thus resulting in better contour-following performances.

Contour Tracking Control of Networked Motion Control System Using Improved Equivalent-Input-Disturbance Approach

This article deals with contour tracking control of a networked multiaxis motion control system with repetitive tasks. To improve the control performance of the system under the overall effects of aperiodic time-varying delays and exogenous disturbances, a network-induced delay is first modeled to be a disturbance. Next, an improved equivalent-input-disturbance (IEID) approach is devised to suppress the overall effect. Then, an iterative learning controller is designed in combination with the IEID estimator to perform individual-axis tracking control. The stability of the system is analyzed using the separation theorem. After that, a cross-coupled controller is used to further improve the contour-tracking performance. Finally, simulations and experiments are carried out to verify the feasibility and effectiveness of the new approach.

Synchronization and stability control of dual-motor intelligent steer-by-wire vehicle

In order to improve the safety of steer-by-wire (SBW) system, a dual-motor SBW system is proposed to enhance the fault tolerance and reliability of the system. However, the dual-motor SBW vehicle often loses its stability due to the external interference, and the asynchronous response between the dual-motor will further deteriorate the stability of the vehicle. Aiming at the existing problems, this paper proposes a hierarchical control strategy, in which the upper layer controls the vehicle stability and the lower layer controls the synchronization of the dual-motor. Firstly, the models of dual-motor SBW system and the vehicle are established. Secondly, considering the interference of lateral wind, sensor noise and the limitation of control output, a yaw rate controller is designed in the upper layer based on the mixed H2/H∞ robust control theory to improve the stability and tracking performance of the vehicle. Thirdly, a sliding mode speed synchronization control strategy is proposed in the lower layer based on the cross-coupling control structure and the sliding mode control algorithm to enhance the synchronization performance between the dual-motor. Finally, the simulation is carried out by using Carsim/Simulink and the hardware-in-the-loop experiment is conducted based on the dual-motor SBW experimental station. The simulation and experimental results verify the effectiveness of the control strategy proposed in this paper.

Contour Tracking Control Based on Extended State Observer for Multiaxis Motion System

In the contouring process, the trajectory generated by the computer numerical control (CNC) machine tool is a result of the multiaxis coordinated motion. The contour error has a direct impact on the accuracy of the machined product. To obtain higher contouring accuracy of the multiaxis motion control system, this paper presents a cross-coupled control approach based on the extended state observer sliding mode control. First, a single-axis sliding mode controller is designed, and an extended state observer is used to estimate system disturbances and improve the system robustness. Then, the cross-coupled control approach handles the coordinated motion of multiple axes to improve the contour control accuracy. Next, a simulation study is conducted on the three-axis motion platform. Its result shows that the control algorithm is effective in reducing tracking errors and contour errors.

Double Propellers Synchronous Control Based on Cross-coupling Control for Buoyancy-lifting Aircraft

To solve the double propellers synchronous control problem of the buoyancy-lifting aircraft, a control approach which uses cross-coupling method to control the double propellers is proposed. Firstly, the lateral-directional stability and manoeuvrability of this type of aircraft with double propellers are analyzed. Secondly, the cross-coupling control method is used to study the speed synchronization performance of the double propellers to improve the control accuracy. The simulation results show that, the double propellers speed synchronization control system based on the cross-coupling control method has a good control performance and better anti-disturbance. Finally, based on the control theory, the cross-coupling controller of the buoyancy-lifting aircraft with double propellers was designed, and ground run test and flight test are carried out. The experiment results show that the control method proposed has better performance and resistance.

X—Y Platform Synchronous Control with CANopen

An X—Y platform synchronous control with CANopen is proposed in this paper, and the platform includes a three-phase stepping motor, motor controller and driver. The Controller Area Network (CAN) Bus is adopted for communication, and the CANopen protocol is also implemented for control. Moreover, both CiA301 standard for communication and CiA402 standard for motor control are support. The interpolation mode in CiA402 is used for synchronized control of the X—Y platform, however, Cross-Coupling Control (CCC) is proposed to improve the precision of synchronized control. The experimental results show the proposed CCC perform higher accuracy than interpolation control. The phenomenon of more position error when higher speed is also discussed.

A Novel Tension Control System of Square Lithium Battery Laminated Machine

Background: To the problem that the traditional square laminated machine with passive unwinding control strategy makes the tape speed periodical changing in reciprocating motion and not achieve a good tension control, a novel unwinding system and control algorithm are presented to improve the efficiency and quality of such equipment. Methods: Compared with the traditional passive unwinding control system, the novel tension control system adds an active compliance mechanism. After obtaining the motion relationship between the compliance device and the laminated motion platform through building the complex system mathematical model, the laminated machine tension control is equivalent to a spatial trajectory tracking control, and multi-axis synchronous coordinated control algorithm is used to control their relative motions, and a cross-coupling control in multi-axis coordinated motion is presented to decrease the synchronous error of the two linear servo motors, which are the compliance device driving motor and the laminated motion platform driving one. Without tension sensor, however, good tension control is obtained only by position tracking control. Results: Based on the proposed approaches and novel unwinding mechanism, the tension control was examined on an experimental square lithium battery laminated machine and results of the experiments performed with the experimental setup demonstrated the effectiveness of the proposed approach. Conclusion: Without a tension sensor, good tension control is obtained only by position tracking control in the novel unwinding system, and the production quality and efficiency of the lithium battery laminated machine are improved.

Cross-Coupled Repetitive Control of a Compliant Nanomanipulator for Micro-Stereolithography

This paper proposes an easy-implemented and high precision contouring control method for a self-developed compliant nanomanipulator supporting cost-effective micro-stereolithography (MSL). The proposed contouring control method is composed of a repetitive controller (RC) to achieve periodic trajectory tracking for each axis, and a cross-coupled control (CCC) for the coordination of contour errors. It is worth noting that the cross-coupled controller design and its integration to RC are not straightforward, as an incorrect feedback position may even deteriorate the contouring and an inappropriate design of the cross-coupled controller leads to instability of the system. For the proposed control structure, a correct feedback position is designed, hence a cross-coupled controller is constructed to ensure the stability and contour error reduction. Various simulations and real-time experiments are deployed on the nanomanipulator, and the comparative results validate the enhanced contour tracking performance of the proposed control method with the contour error 86 nm.

Research on a Multi-Motor Coordinated Control Strategy Based on Fuzzy Ring Network Control

Aiming at the multi-motor coordinated control of intelligent robots, cross-coupling ring control based on fuzzy theory (CRCF) is proposed. Each motor is cross-coupled with two adjacent motors to form a multi-motor ring network structure that eliminates lag in speed tracking between motors and enhances synchronization between motors. Applying fuzzy control to the cross-coupling control of the proposed control strategy, the speed error and change in speed error of two adjacent motors are used as the input of the fuzzy controller, and its output is used as the input of the second of the two adjacent motors. The fuzzy controller achieves real-time tracking adjustment of the speed error between motors. The controllability and observability of the proposed control strategy are verified by the theorem of the Kalman matrix rank criterion. The external stability and internal stability are verified using an impulse response matrix. The theoretical analysis of the lag is verified by establishing a physical and mathematical model. Finally, a four-motor coordination control system model is built. By comparison with the non-ring network proportional cross-coupling control method, the effectiveness of the proposed control strategy is experimentally verified by the MATLAB/Simulink and the RT-LAB real-time simulation platform.

Grid-Connected Harmonic Current Suppression of Permanent Magnet Direct Drive Wind Power Converter Based on Current Cross-Coupling Control

Due to the power-grid low-order harmonic voltage and the nonlinearity of power electronic devices, the grid-connected converter of wind power generation system produces grid-connected harmonic current. In order to improve the output power quality of full-power grid-connected converter of wind power generation system, based on the detailed analysis of the harmonic mathematical model of grid-side converter, a cross-coupling control strategy for suppressing the low-order harmonic current components is proposed in this paper. In this control strategy, the DC component of each grid-connected harmonic current is detected in the multi-synchronous rotating coordinate system, and the current cross-coupling control method is adopted to realize the accurate control of each harmonic current. The harmonic current cross-coupling controller is analyzed and designed in detail. The proposed control strategy takes into account the cross-coupling effect of each harmonic current, which can effectively reduce the interaction between each harmonic current and the fundamental current, and improve the stability of the system. Simulation and experimental test verify the correctness and feasibility of the proposed control strategy.

A Cross Coupling Control Strategy for Dual-Motor Speed Synchronous System Based on Second Order Global Fast Terminal Sliding Mode Control

A cross coupling control strategy based on second-order global fast terminal sliding mode control(2-GFTSMC) is proposed in this paper aiming to improve the synchronization accuracy of dual-motor under external load and disturbance. Firstly, the global fast terminal sliding mode controller is designed to improve the starting performance and dynamic performance of single motor and eliminate chattering phenomenon. Secondly, in order to improve the synchronization accuracy, enhance the stability of the dual-motor system and shorten the response time, a second-order global fast terminal sliding mode controller is designed by combining the global fast terminal sliding mode control with the cross-coupling control strategy. Finally, an experimental platform of dual-motor synchronous control is built, and the effectiveness of the proposed synchronization control strategy is verified by experiments.

Motor synchronisation control for multistage hot die forging press feed manipulator based on BP-PID controller

The rapid development of the automotive industry provides a great opportunity for the development of the forging industry. The multistage precision hot die forging is widely used across the world. In order to improve production efficiency, reduce labour costs, and realise the production automation, a multistage hot die forging press feed manipulator is designed in this paper. The mechanical structure is designed firstly. Then the multi-motor synchronisation control problem is also studied. Based on the adjacent cross-coupling control structure, the BP neural network-PID control algorithm is proposed. Simulation and experiment results show that the BP-PID controller has high control accuracy, a fast convergence speed, and can achieve multi-motor synchronous control effectively. The manipulator designed in this paper has a high practical application value.

Research on the process technique of electrical discharge machining based on dual-linear motors

In order to research the electrical discharge machining（EDM） process of the dual-linear motors driving system, in this paper, a dual-linear motor driving spindle structure with balance cylinder is proposed, in which the cross-coupling control algorithm is used to control the dual-linear motors.This structure and control method can improve the thermal balance of the spindle, and availably reduce the influence of the motor heating on the accuracy. In this paper, the method of simulation analysis and positioning detection is applied to verify the effectiveness of the design. Furthermore, the machining ability of dual-linear motors EDM and the ball-screw EDM spindle are compared through efficiency discharging process test and mirror process test. By the comparative results, the dual-linear motors driving technique in EDM filed has higher machining efficiency. The tests results show that the EDM database of the ball-screw EDM spindle can be replaced by dual-linear motors EDM spindle seamlessly. So the dual-linear motors driving technique is suitable for the EDM process.

A Cross-Coupled Control Strategy of Phase Difference for Electric Vibration Damping Actuator

The active vibration damping actuator uses dual-motors to drive two sets of eccentric wheels to achieve active vibration reduction, but the backlash nonlinearity and eccentric load will cause the load speed and load position to be out of synchronization, which will influence the system vibration reduction effect. The traditional parallel control strategy controls the dual motors separately without the consideration of internal coupling effect, leading to a poor synchronization performance. In order to solve these problems, a load position difference cross-coupled control strategy based on multiple-input and multiple-output (MIMO) is proposed in this paper. The minimum singular value of return difference matrix is used to analyze the stability margin of active vibration damping actuator system under the traditional parallel control strategy and the cross-coupled control strategy, and the analysis procedure has considered the influences of load disturbance and backlash nonlinearity. At the same time, the sensitivity comparison of the two strategies is conducted, and the results indicate that the system under cross-coupled control strategy has stronger relative stability and robustness. On this basis, a method for designing synchronization controller parameters is given. The stability region of parameters satisfying the requirement of stability margin is determined with the help of minimum singular value of return difference matrix. Then, the optimal value is found in the obtained parameter stability region according to the dynamic and steady-state performance. Finally, an experimental platform is set up to verify the effectiveness of cross-coupled control strategy and the rationality of parameter tuning.

Precise Linear-Motor Synchronization Control Via Cross-Coupled Second-Order Discrete-Time Fractional-Order Sliding Mode

This article presents a universal method of precise synchronization control for linear-motor-driven systems. The control method named cross-coupled second-order discrete-time fractional-order sliding mode control contains a cross-coupled control strategy to reduce the incoordination among driving linear motors. It also includes the second-order structure and fractional-order sliding mode surface to reduce the chattering phenomenon and improve the dynamic performance simultaneously, so that the precision is further enhanced. In particular, a universal definition of synchronization error is presented so that a better synchronization control performance can be achieved, especially in multidimensional systems. It is also compatible well with the contouring control, which extends the application further. Moreover, the stability of the controller is analyzed in this article. Finally, the proposed control method is conducted in simulations and experiments under various tasks, whose results have proved its effectiveness and advantages over conventional methods.

Second-Order Sliding-Mode-Based Synchronization Control of Cable-Driven Parallel Robots

Cable-driven parallel robots (CDPRs) can provide a high speed and a heavy payload in a large workspace. The main challenge of the CDPRs stems from the dynamic control, in which all the cables must coordinate with each other to remain in tension, and the cable-driven form may lead to model uncertainties. To solve it, the second-order sliding mode (SOSM) is combined with the multicable synchronization idea to propose a new SOSM-based synchronization control (SOSM-SC) strategy for the CDPRs. The goal of the cross-coupled control approach is to improve the synchronization motion relationship between all the cables and guarantee better trajectory tracking control, whereas the SOSM can restrain the model uncertainties and external disturbances. The Lyapunov theory is utilized to prove the asymptotic stability of the closed-loop control system of CDPRs. Trajectory tracking experiments indicate that compared with the existing synchronization control strategy and the augmented proportional-derivative strategy, the proposed SOSM-SC strategy significantly reduces the cable tracking error and the cable synchronization error, and ultimately improves the control accuracy for the mobile platform. The tracking experiments of the antidisturbance indicate that the SOSM-SC strategy can retain good tracking accuracy under external disturbances.

Iterative Learning Synchronized Control of Multi-leaf Collimator Based on Cross-coupled Control

Iterative Learning Synchronized Control of Multi-leaf Collimator Based on Cross-coupled Control