Servo Performance Research Articles

Research on Simulation Analysis of Valveless Hydraulic Servo System

The hydraulic transmission technology is widely used in the industrial field. With the continuous development of microelectronic technology, valveless electro-hydraulic servo technology came into being. Aiming at the problems such as slow response speed and poor displacement tracking accuracy, this paper builds a simulation model of the forward and reverse displacement of the valveless electro-hydraulic servo system, and uses AMESim and simulink software to build the hydraulic part simulation and motor part simulation of the system respectively. A fuzzy PID controller is introduced and simulation is performed with the addition of the fuzzy PID controller to improve the overall performance of the valveless electro-hydraulic servo system.

Improved Control for Industrial Systems Over Model Uncertainty: A Receding Horizon Expanded State Space Control Approach

In this paper, an improved linear quadratic tracking control strategy using a new receding horizon expanded state space (ESS) model is proposed. Unlike traditional state space model, the new ESS model first facilitates the combination of the system state variables and tracking errors, then a subsequent new receding horizon improved linear quadratic tracking control (RHLQTC) is designed with more degrees of freedoms for the adjustment of control parameters, which yields improved control performance compared with traditional RHLQTC. Finally, simulations on a typical reverse process are done in comparison with traditional RHLQTC in terms of both servo and regulatory performance, where results show that the proposed controller provides improved performance under both situations.

Continuous sliding mode control for gun position servo system

With the development of military technology and changes in the war situation, modern warfare has higher requirements for the accuracy and speed of gun firing. The control performance of the gun position servo system directly affects the accuracy and speed of the gun firing. In order to improve performance of the gun, the sliding mode control is investigated for the gun position servo system. Sliding mode control has advantages of simple structure and good robustness against uncertain system parameters and disturbance. But discontinuous sign function in the classical sliding mode control method will lead to chattering of the system. To address the shortcoming of chattering in the traditional sliding mode control, a continuous sliding mode control algorithm is investigated in this paper. Finally, numerical simulations are performed to illustrate the efficiency of the theoretical results.

Parametric Optimization of Electrohydraulic Servo System

The electrohydraulic servo systems used in the industrial production are characterized by relatively simple construction, easy operation and high speed, good reliability, functional flexibility and low cost. All this demonstrates the need to study the performance of electrohydraulic servo system primarily in dynamic operating modes. The article studies a mathematical model of electrohydraulic servo system with the typical nonlinearities. The parametric optimization of the automatic PID controller was performed on the basis of minimizing the integral quality criterion when comparing reference and experimental transient processes. The obtained results are shown in a graphical form.

Design and development of modified RTD-A controller for unstable bioreactor

Control of open loop unstable process is a challenging one owing to the presence of right hand plane pole(s). The spotlight of this paper is to develop modified Robustness set point Tracking Disturbance rejection and Aggressiveness controller(RTD-A) for an unstable process. The RTD-A controller formulation is modified accordingly to suit the unstable process. The proposed control scheme has two control loops. The unstable process is initially stabilized by an inner feedback loop consisting of a proportional controller. The RTD-A control strategy is then implemented on the stabilized plant. The developed control scheme is validated on an nonlinear unstable bioreactor plant model in a simulation environment. It is found that the proposed controller has better servo and regulatory performance when compared to the conventional IMC-PID controller. Effect of variation in the tuning parameters of the controllers on the process output is analysed in detail.

Research on the Method of Suppressing the End Detent Force of Permanent Magnet Linear Synchronous Motor Based on Stepped Double Auxiliary Pole

Permanent magnet linear synchronous motors have the advantages of high thrust density, high acceleration, high speed, and high efficiency, which are widely used in CNC lathes, lithography machines, rail transportation, etc. In high-speed, high-precision servo control systems, detent force fluctuation caused by end effect can easily cause problems such as speed fluctuation, mechanical vibration and electromagnetic noise, which affect the servo performance of permanent magnet linear synchronous motors. Aiming at the detent force fluctuation caused by the end effect of permanent magnet linear synchronous motor, this paper proposes a stepped double auxiliary pole method. The method has a good suppression effect on the end normal force fluctuation and the end thrust fluctuation, which improves the servo performance of the permanent magnet linear synchronous motor in the high-precision servo system. In the traditional methods of suppressing the fluctuation of end detent force, two common methods are using a magnetic isolation aluminum plate and optimizing the auxiliary pole size. The former needs a magnetic isolation aluminum plate to connect the auxiliary pole and the primary mover. Therefore, it needs to add the connection device to connect those three parts. The connection device complicates the auxiliary pole part and increases manufacturing difficulty. The latter does not change the manufacturing process, but in the early design process, the optimum size of the auxiliary needs to be considered. Compared with these two methods, the one proposed in this paper avoids the complex structure of magnetic isolation aluminum plate, the stepped double auxiliary pole is integrated with the primary mover. Moreover, it has a fixed structure with optimum size. Therefore, the method in the paper does not change the manufacturing process, improves the strength of the initial pole structure, and reduces design period. Finally, the finite element analysis by ANSYS was performed to illustrate the correctness and effectiveness of the method.

Data-Based Iterative Dynamic Decoupling Control for Precision MIMO Motion Systems

Decoupling control is still an important research topic for precision multiple-input–multiple-output (MIMO) motion systems involved in computer numerically controlled (CNC) machine tools, wafer scanners, etc. In this paper, to minimize internal coupling and improve servo performance, a data-based iterative dynamic decoupling control (IDDC) approach is synthesized. Specifically, a MIMO dynamic decoupling controller structured with finite impulse response filter is used as an add-on to a static decoupling part. Then, a data-based parameter optimization algorithm is developed such that the optimal parameters can be iteratively solved based entirely on the input/output data by minimizing the coupling-induced error. Unlike pre-existing IDDC approaches, the proposed approach can achieve an unbiased estimate of the optimal parameters combined with a small estimate variance that is illustrated through numerical simulation. Finally, application to an ultraprecision wafer stage confirms that the proposed approach significantly decreases the coupling-induced error and achieves enhanced performance compared to pre-existing approaches.

Design of Centralized PI Control System for Two Variable Processes based on Root Locus Technique

This paper describes the design of centralized controller for two variable processes. The two variable process structures are somehow different from the single variable processes. This difference is occurred because of interrelations between the variables present in the process. Hence, when a controller is planned for such systems, the relations amid the variables must be taken into consideration. This process is done in decentralized control system design. But decentralized control system works well when the interrelations between the variables are simple. If the interaction is strong, then the centralized control system is preferred since it uses a controller for each pair of input and output variables. The controller used in main diagonal works for improving the servo performance and off diagonal controller reduces the interrelation effect. So the performance is improved by minimizing the interrelation effects. The design process is easy to understand by field engineers working in industries. The simulation results are included in this paper to specify the efficacy of the proposed scheme.

Data-Based Switching Feedforward Control for Repeating and Varying Tasks: With Application to an Ultraprecision Wafer Stage

In precision motion systems, well-designed feedforward control can effectively compensate for the reference-induced error. Compared to iterative learning control (ILC), data-based fixed-structure feedforward control (DFFC) possesses robustness against reference variations, but results in mediocre performance in exactly repeating tasks. In this paper, a novel data-based switching feedforward control (DSFC) approach is synthesized to well balance the tradeoff between the extrapolation capabilities and servo performance. Specifically, a theoretical framework is developed for the proposed DSFC approach, where the feedforward control is switched between ILC and DFFC according to whether the successive references are repeated or not. When operating in the DFFC mode, a new iterative parameter tuning algorithm is proposed to enable the performance enhancement compared to the pre-existing DFFC and overcome the limitation of the allowable reference variations. Furthermore, an unbiased estimate method for the convolution matrix of the (process) sensitivity function is developed based on the impulse response experiment. No parametric model is required throughout the proposed DSFC procedure, and the optimal parameters of the DFFC mode can be unbiasedly estimated. Experimental results on an ultraprecision wafer stage confirm that the proposed DSFC combines advantages of ILC and DFFC, and achieves high performance for both repeating and varying tasks.

Backstepping Adaptive Neural Network Control for Electric Braking Systems of Aircrafts

This paper proposes an adaptive backstepping control algorithm for electric braking systems with electromechanical actuators (EMAs). First, the ideal mathematical model of the EMA is established, and the nonlinear factors are analyzed, such as the deformation of the reduction gear. Subsequently, the actual mathematical model of the EMA is rebuilt by combining the ideal model and the nonlinear factors. To realize high performance braking pressure control, the backstepping control method is adopted to address the mismatched uncertainties in the electric braking system, and a radial basis function (RBF) neural network is established to estimate the nonlinear functions in the control system. The experimental results indicate that the proposed braking pressure control strategy can improve the servo performance of the electric braking system. In addition, the hardware-in-loop (HIL) experimental results show that the proposed EMA controller can satisfy the requirements of the aircraft antilock braking systems.

Reliable Tracking Control for Under-Actuated Quadrotors With Wind Disturbances

This paper presents a reliable control strategy for quadrotors to achieve a satisfactory tracking performance and provide a stable yaw angle control in the presence of wind disturbances. Based on the prelinearizing transformation and singular perturbation techniques, a quadrotor flight system is decomposed into two interconnected subsystems in different time-scales: 1) the angular rotations and 2) the linear translations. For the fast subsystem running as the inner loop, finite frequency H∞ control is used to enhance robustness and provide adequate decoupling such that each translational dynamic is controlled independently. For the slow subsystem running as the outer loop, H∞ loop shaping control via proportion-integration-differentiation control is used to achieve a desired servo performance even in the presence of wind disturbance. Simulations are performed under different wind conditions to validate the effectiveness of the new control strategy.

Control of Integrating Process with Time Delay

Abstract This paper addresses the control of integrating processes with time delay. Two different control structures, namely single feedback loop (SFBL) and double feedback loop (DFBL) have been considered. In the SFBL, the controller has been designed using direct synthesis approach for the desired regulatory performance. In the DFBL, the inner loop controller is the proportional only controller which stabilizes the inner loop. The outer loop controller of DFBL has been designed through direct synthesis approach to achieve desired servo performance. Both the proposed control scheme works satisfactorily for low order as well as high order integrating process which may have a time delay and inverse response dynamics. Simulation of various examples shows improved performance when compared with the recently reported method.

Dual-valve parallel prediction control for an electro-hydraulic servo system.

To improve the dynamic response performance of a high-flow electro-hydraulic servo system, scholars have conducted considerable research on the synchronous and time-sharing controls of multiple valves. However, most scholars have used offline optimization to improve control performance. Thus, control performance cannot be dynamically adjusted or optimized. To repeatedly optimize the performance of multiple valves online, this study proposes a method for connecting a high-flow proportional valve in parallel with a low-flow servo valve. Moreover, this study proposes an algorithm in which a proportional-integral-derivative system and multivariable predictive control system are used as an inner loop and outer loop, respectively. The simulation and experimental results revealed that dual-valve parallel control could effectively improve the control accuracy and dynamic response performance of an electro-hydraulic servo system and that the proportional-integral-derivative-multivariable predictive control controller could further dynamically improve the control accuracy.

Study on dual redundant PMSM drive design and fault-tolerant control strategy

ABSTRACTWith the development and application of servo system, the requirements of high performance servo system are getting higher and higher. Its key is the high-performance motor that has the fault-tolerance to improve the motor reliability. This paper proposes a novel dual redundant PMSM (Permanent magnet synchronous motor), which has multiple same armature winding. Each winding has same three phases and is controlled by inverter module. Based on the fault-tolerant control system model, a reliable fault-tolerant control strategy has been proposed. The experiment platform is built to carry out consistency experiment of each redundancy, response characteristic experiment and fault-tolerant experiment of two redundancies in the PMSM. The experiment result shows the dual redundant PMSM has a good response and fault-tolerance characteristics.

Integrated Position and Speed Loops Under Sliding-Mode Control Optimized by Differential Evolution Algorithm for PMSM Drives

In this paper, to improve the robustness and realize the precision positioning as well as speed control of the servo drive system, an integrated sliding-mode control (ISMC) optimized by differential evolution (DE-ISMC) algorithm is proposed. ISMC guarantees that a motor can reach at given position with given speed, and given speed is set first. ISMC, which is combined with speed regulator and position regulator, is different from the conventional sliding-mode control (SMC) replacing speed regulator. ISMC can guarantee that motor speed is controlled under position control mode, which is a novelty and an advantage of ISMC in this paper. To achieve good control performance of ISMC, parameters of it should be chosen exactly, so DE algorithm is selected to optimize them. The most significant influence factor of DE algorithm is the optimization iteration. Once parameters of ISMC are optimized under convergent iteration, servo system performance reaches given indices in the shortest time. Experimental results indicate that robustness of the servo system is improved; correctness and effectiveness of DE-ISMC are verified.

PID Controller Design for Tito Processes Based on IMC and Smith Predictor Configuration

This paper describes the design of Proportional-Integral-Derivative (PID) controller for two variable processes where the two variables need to control. Design of controllers for such a process is too difficult than single variable processes because of interrelations between the two variables present in the system. Hence, the design approach should include the interrelations of the variables to achieve better performance of the processes. In addition to this, the time delay of the processes is also considered and Smith Predictor (SP) configuration is used to reduce the delay in the processes. For the resultant reduced time delay processes, an IMC approach is used to design PID controller. The proposed control system improves both the servo (set point tracking) and regulatory (disturbance rejection) performance of the system. The proposed configuration is also validated using a case study. The simulation results are presented and compared with the other similar approaches to show the efficacy of the proposed method.

Discrete-Time First-Order Plus Dead-Time Model-Reference Trade-off PID Control Design

The present study proposes a novel proportional-integral-derivative (PID) control design method in discrete time. In the proposed method, a PID controller is designed for first-order plus dead-time (FOPDT) systems so that the prescribed robust stability is accomplished. Furthermore, based on the control performance, the relationship between the servo performance and the regulator performance is a trade-off relationship, and hence, these items are not simultaneously optimized. Therefore, the proposed method provides an optimal design method of the PID parameters for optimizing the reference tracking and disturbance rejection performances, respectively. Even though such a trade-off design method is being actively researched for continuous time, few studies have examined such a method for discrete time. In conventional discrete time methods, the robust stability is not directly prescribed or available systems are restricted to systems for which the dead-time in the continuous time model is an integer multiple of the sampling interval. On the other hand, in the proposed method, even when a discrete time zero is included in the controlled plant, the optimal PID parameters are obtained. In the present study, as well as the other plant parameters, a zero in the FOPDT system is newly normalized, and then, a universal design method is obtained for the FOPDT system with the zero. Finally, the effectiveness of the proposed method is demonstrated through numerical examples.

PID Controller Design for TITO Processes Based on IMC and Smith Predictor Configuration

This paper describes the design of ProportionalIntegral-Derivative (PID) controller for two variable processes where the two variables need to control. Design of controllers for such a process is too difficult than single variable processes because of interrelations between the two variables present in the system. Hence, the design approach should include the interrelations of the variables to achieve better performance of the processes. In addition to this, the time delay of the processes is also considered and Smith Predictor (SP) configuration is used to reduce the delay in the processes. For the resultant reduced time delay processes, an IMC approach is used to design PID controller. The proposed control system improves both the servo (set point tracking) and regulatory (disturbance rejection) performance of the system. The proposed configuration is also validated using a case study. The simulation results are presented and compared with the other similar approaches to show the efficacy of the proposed method

A New Load Torque Identification Sliding Mode Observer for Permanent Magnet Synchronous Machine Drive System

Effective identification of the load torque is one of the key aspects in improving the performance of servo drive systems against load disturbances. Sliding mode variable structure control has become a popular method in the development of a load torque identification (LTID) algorithm due to its parameter insensitivity and easy realization features. However, existing LTID sliding mode observers (SMO) with conventional structure have the disadvantages of high-frequency chattering and poor estimation accuracy, which limit its application in high-performance servo systems. In this paper, the mathematical model of the conventional LTID-SMO is deduced and analyzed. A new LTID-SMO is proposed by replacing the sign function with a saturation function and an additional feedback loop in the load torque observer. The effectiveness of the proposed observer is verified by various experiments. The results show that compared to conventional load torque observer, the proposed observer can identify the load torque with higher accuracy and faster response in different operational conditions.

A robust weld seam recognition method under heavy noise based on structured-light vision

Abstract Structured-light vision systems are widely used in robotic welding. The key to improving the robotic visual servo performance and weld quality is the weld seam recognition accuracy. Common detection algorithms are likely to be disturbed by the noise of spatter and arc during the welding process. In this paper, a weld seam recognition algorithm is proposed based on structured light vision to overcome this challenge. The core of this method is fully utilizing information of previous frames to process the current frame, which can make weld seam extraction both more robust and effective. The algorithm can be divided into three steps: initial laser center line recognition, online laser center line detection, and weld feature extraction. A Laplacian of Gaussian filter is used for recognizing the laser center line in the first frame. Afterwards, an algorithm based on the NURBS-snake model detects the laser center line online in a dynamic region of interest (abbreviated ROI). The center line obtained from first step is set as the initial contour of the NURBS-snake model. Using the line obtained from the previous step, feature points are determined by segmentation and straight-line fitting, while the position of the weld seam can be calculated according to the feature points. The accuracy, efficiency and robustness of the recognition algorithm are verified by experiments.