Model Of Servo System Research Articles

Control system design for pneumatic surgical robot under MRI environment

Objective To design the control system of a magnetic resonance image (MRI) navigated pneumatic surgical robot. Method The driven system of the robot was constructed by combining with pneumatically driven and ultrasonic motor. The cylinder position control loop was established based on proportion integration differentiation (PID) control. The mathematical model of the pneumatic servo system was established by system identification. The PID parameter tuning and the simulation of the system characteristics were conducted. The stability analysis was conducted using the Nyquist criterion, and the acupuncture accuracy and the magnetic compatibility of the robot were verified. Results The simulation results showed that the maximum steady-state error was about 0.4 mm and the maximum tracking error was less than 2 mm, indicating that the PID control system had high control precision and trajectory tracking ability. The error of the acupuncture accuracy test was 0.72 mm. The results of water-modeling experiments showed that the magnetic resonance images were clear indicating that the influence of the robot on the MRI images was small. Conclusions The results of imulation, acupuncture and water-modeling tests showed that the pneumatic robot system can meet the requirements of brachytherapy surgery. Key words: Magnetic resonance imaging; Surgical robot; Pneumatic control system; PID control

Modeling and identification of hydraulic servo systems

The goal of this research is to implement a nonlinear simulation model of hydraulic servo system (HSS).The model is based on physical laws as well as experimental identification of piston position. It also presents the tuning of PID/PI controller’s parameters using particle swarm optimization technique. The mathematical model includes the most nonlinear effects that are involved in the hydraulic system under study. The dynamics of hydraulic systems are highly nonlinear due to directional change of valve opening, friction forces, and oil compressibility. The model describes the behavior of a servo system BOSCH REXROTH servo valve (4WRSE). It has been developed using MATLAB/SIMULINK. The main objective of the simulation modeling and system identification for electro-hydraulic servo valve is to obtain good performance of its dynamic and nonlinear behavior. The identified model has been found to be a third-order continuous time model. The identification of HSS is performed by using System Identification Toolbox of MATLAB. The obtained results are promising and satisfactory. In addition, the simulation and experimental results have shown the superiority of using PID controller type for requirement of minimum settling time and the PI controller type for minimum value of percentage overshoot.

Dynamic characteristics for a hydro-turbine governing system with viscoelastic materials described by fractional calculus

• A fractional-order model of the hydraulic servo system is proposed. • The proposed model can be used for the hydro-turbine governing system with order uncertainty. • Fractional nonlinear dynamic characteristics are analyzed. • Changing law of some key points are presented. This paper brings attention to the dynamic characteristics of a hydro-turbine governing system with viscoelastic materials. Fractional calculus is introduced to established a diversified nonlinear mathematical model of a hydro-turbine governing system, considering the memory characteristic of the viscoelastic materials of the hydraulic servo system. Furthermore, the effect of different fractional orders on the generator speed is studied by analysis of fractional bifurcation diagrams, time waveforms, phase orbits, Poincare maps, power spectrums and spectrograms. Fortunately, some motion laws of the bifurcation points and chaotic regions with the increase of fractional order α are obtained, and the safe range of k d with different fraction order is presented. All of the above results provide a sound theoretical basis for designing and running of the hydro-turbine governing system.

Mathematical modeling of servo system of industrial robot

Mathematical modeling of servo system of industrial robot

Composite Decoupling Control of Gimbal Servo System in Double-Gimbaled Variable Speed CMG Via Disturbance Observer

In order to realize the decoupling and disturbance rejection control of the inner and outer gimbal system under two working conditions of a double-gimbaled variable speed control moment gyroscope (DGVSCMG), this paper presents a composite controller based on the disturbance observer and state feedback control. We first developed a dynamic model of a double-gimbal servo system, and analyzed the system characteristics of coupling and mismatched disturbance in CMG and flywheel working modes. Then, we propose a novel decoupling method through regarding the coupling term as systems lumped disturbance. The system disturbance was estimated by the designed disturbance observer and was rejected via the proposed composite controller combining a state feedback method. Finally, we proved the overall system stability by using a Lyapunov approach and derived an estimated upper bound of the state variables to guide controller parameters selection. We concluded from simulation and experimental results that the proposed method was effective in decoupling and disturbance compensation control of the DGVSCMG double-gimbal servo system, and enhanced system disturbance rejection and speed servo performance.

Modeling and Control of the CSCEC Multi-Function Testing System

In order to promote the research and development on evaluating the seismic performance of structures, China State Construction Engineering Corporation (CSCEC) planned to construct a large-scale loading testing facility, the Multi-Function Testing System (MFTS). This facility can perform full-scale, real-time, 6-degree-of-freedom static and dynamic testing of rubber bearings and many types of structural components including long columns, shear walls and cross shape joints. The basic performances of the MFTS are a clearance of 9.1 m × 6.6 m × 10 m for specimen installation, maximum x-directional displacement 1500 mm, maximum y-directional velocity 1570 mm/s and maximum z-directional compressive load 108 MN. The system configuration and performance specifications of the MFTS are presented in this paper. The inverse kinematics model and the nonlinear model of the hydraulic servosystem of the MFTS are built. A modified feedback forward kinematics algorithm is developed for real-time control of the MFTS. Internal force characteristics of the loading system are analyzed. The internal force control method based on real-time solution of basis of internal force space is proposed for the system with large motion ranges. The motion controller combining position control loop and internal force control loop is developed. To meet the requirement of simultaneously imposing vertical compressive load and horizontal displacement, a mixed load and displacement controller is designed, where a direct force control loop is used to improve the response speed of the force control and reduce spatial dynamic coupling effects. Finally, a dynamic bearing testing is performed. The test results demonstrate that the system using the proposed controller has good abilities on position tracking, force balance, and load following.

Design and analysis of mechanic-hydraulic servo control steering system for pure rolling in multi-axle vehicle

With more axles for multi-axle vehicles, conventional steering trapeziums are unable to let every tire fit Ackermann steering which cause tire wear increasingly more serious. To alleviate this problem, an original mechanic-hydraulic servo steering system with a controllable tie rod is designed. By controlling the angle of one wheel and the length of tie rod, both wheels can be controlled as per default trajectory which implemented Ackermann steering. This article utilized mechanic-hydraulic servo feedback to design a mechanic-hydraulic servo valve which controlled the tie rod accurately. It ensured dynamic characteristics of steering wheels and driving force. To understand inherent characteristics of system, the mathematical model was established. The transfer function was derived, and this high-order system was reduced by Routh approximation. Analyzed natural frequency and the main parameter (the gain coefficient of displacement) which influences the dynamic characteristics had been found out. Analysis shows that the lower the gain coefficient, the higher the speed of response. Moreover, the accurate simulation model of servo system is built on AMESim. Contrasting five groups of simulation results, it is obtained that the influence rule of the gain coefficient is consistent with theoretical analysis. This research provides a useful reference for future nonlinear control.

Theoretical and experimental analysis of an optical driven servo system

An optical driven servo system model based on single-type PLZT ceramic is proposed in this paper. The control equation of the proposed servo system is derived based on the mathematical model of PLZT with coupled multi-physics fields. The parameters of photodeformation of the PLZT actuator during both the illumination phase and light off phase are identified through the static experiment. Then displacement response of optical driven servo system is numerically simulated based on the control equation presented in this paper. After that, the closed-loop control experiment of optical driven servo system based on PLZT single-type ceramic with a simple on–off method is carried out. The experimental results show that the optical driven servo system with simple on–off method can achieve the target displacement by applying UV light to the PLZT actuator. Furthermore, an improved on–off control strategy is proposed to decrease the undesirable fluctuation around the target displacement.

Global dynamic modeling of electro-hydraulic 3-UPS/S parallel stabilized platform by bond graph

Dynamic modeling of a parallel manipulator(PM) is an important issue. A complete PM system is actually composed of multiple physical domains. As PMs are widely used in various fields, the importance of modeling the global dynamic model of the PM system becomes increasingly prominent. Currently there lacks further research in global dynamic modeling. A unified modeling approach for the multi-energy domains PM system is proposed based on bond graph and a global dynamic model of the 3-UPS/S parallel stabilized platform involving mechanical and electrical-hydraulic elements is built. Firstly, the screw bond graph theory is improved based on the screw theory, the modular joint model is modeled and the normalized dynamic model of the mechanism is established. Secondly, combined with the electro-hydraulic servo system model built by traditional bond graph, the global dynamic model of the system is obtained, and then the motion, force and power of any element can be obtained directly. Lastly, the experiments and simulations of the driving forces, pressure and flow are performed, and the results show that, the theoretical calculation results of the driving forces are in accord with the experimental ones, and the pressure and flow of the first limb and the third limb are symmetry with each other. The results are reasonable and verify the correctness and effectiveness of the model and the method. The proposed dynamic modeling method provides a reference for modeling of other multi-energy domains system which contains complex PM.

Friction compensation of harmonic gear based on location relationship

In the harmonic gear servo system, friction is associated with not only the velocity of the input shaft but also its angle position. Traditional friction compensation based on the velocity cannot guarantee the high motion accuracy. To address this problem, this article proposed a new friction model of harmonic gear servo system, which is related to both its velocity and position. The new model includes two parts: in the presliding region, the static friction is determined by the maximum elastic deformation recovery angle of the input shaft, and in the sliding region, the friction not only has Stribeck effect from velocity but also has harmonic series relative to the input shaft’s position. In this article, the parameters of friction model were obtained by preliminary experiments. A control diagram based on this model was established for friction compensation and the proposed control algorithm showed its superiority in the experiments.

Cross-coupling integral adaptive robust posture control of a pneumatic parallel platform

A pneumatic parallel platform driven by an air cylinder and three circumambient pneumatic muscles was considered. Firstly, a mathematical model of the pneumatic servo system was developed for the MIMO nonlinear model-based controller designed. The pneumatic muscles were controlled by three proportional position valves, and the air cylinder was controlled by a proportional pressure valve. As the forward kinematics of this structure had no analytical solution, the control strategy should be designed in joint space. A cross-coupling integral adaptive robust controller (CCIARC) which combined cross-coupling control strategy and traditional adaptive robust control (ARC) theory was developed by back-stepping method to accomplish trajectory tracking control of the parallel platform. The cross-coupling part of the controller stabilized the length error in joint space as well as the synchronization error, and the adaptive robust control part attenuated the adverse effects of modelling error and disturbance. The force character of the pneumatic muscles was difficult to model precisely, so the on-line recursive least square estimation (RLSE) method was employed to modify the model compensation. The projector mapping method was used to condition the RLSE algorithm to bound the parameters estimated. An integral feedback part was added to the traditional robust function to reduce the negative influence of the slow time-varying characteristic of pneumatic muscles and enhance the ability of trajectory tracking. The stability of the controller designed was proved through Laypunov’s theory. Various contrast controllers were designed to testify the newly designed components of the CCIARC. Extensive experiments were conducted to illustrate the performance of the controller.

Research on AC Servo Motor Load Disturbance Method

For the decline of the control accuracy of servo system due to the disturbances of load, to design the dimensionality reduction load torque observer, the observed value of load torque after conversion for compensation control. Established the three- loop mathematical model of servo control system, to elicit three- loop control parameter setting formula by the application of optimal second order and third order model theory. Established the simulation model of space vector control AC servo system, by simulation experiment it is verified that three-ring parameters can provide good dynamic performance for system after setting. After the establishment of experimental platform, through the motor load sudden change experiment, it proved the feasibility of the torque compensation control for improving the servo system control precision under load disturbances.

Practical behavior of advanced non-linear hydraulic servo system model for a mold oscillating mechanism depending on line volume

We studied a mold oscillating mechanism for continuous casting. An equivalent hydraulic servo system model was established including a non-linear property and line volume near the hydraulic cylinder. The analysis focused on a practical behavior of the system. To observe an oscillated object and dynamic responses, an equivalent stiffness, damping ratio and simple mass-damper-spring 1-DOF model were established by Karl-Erik Rydberg’s research, and showed hydraulic cylinder pressure and line volume near the hydraulic cylinder. Especially, hydraulic pressure including statue of a mechanical and hydraulic cylinder was analyzed in the time and frequency domain. The results were validated by comparing responses between the 1-DOF model and the nonlinear hydraulic servo system model. The line volume that connects the hydraulic cylinder and the hydraulic servo valve has great effect on damping ratio and natural frequency of the hydraulic servo system. When the line pipe has high volume compared to normal statue, the hydraulic cylinder pressure has sharp peak frequencies that are located on natural frequency and its duple-harmonic terms with sideband peaks; (±2×exciting frequency) space. Based on this fact, we investigated the model using sensitivity analysis, and explained an oscillating mechanism about the mold oscillator by applying additional spring. A design of robust control for the mold oscillator was suggested by Negative strip time criterion, and maximum additional spring stiffness was shown.

Nonlinear Servomotor in Single Pulse Simulation of Electrical Discharge Machining System Modeling

<p>Electrical Discharge Machining, EDM is a nonconventional and high precision machining. EDM system is considered a combination of servo system and EDM process. The servo system precisely controls the gap between electrode and workpiece for the continuous electrical discharges occurrence. Machining performance and stability depend on the performance of servo system. The EDM servo system usually modeled as a linear system, which ignores the nonlinearities of the motor. An assumption that the nonlinearities are insignificant in EDM system model may leads to modeling errors and result in poor control performance. In this study, nonlinear EDM servo system model was presented and the dynamic response of the model was analyzed and compared with the linear model. Simulation result shows a slightly difference in system response and a controller used in linear model is less efficient for a nonlinear EDM servo system model. The results are very useful for control strategy and can contribute to a better machining performance and stability of EDM applications.</p>

Dynamics Modeling and Simulation of Mechanical and Servo Systems in Hard Disk Drives

Dynamics Modeling and Simulation of Mechanical and Servo Systems in Hard Disk Drives

Frequency domain modelling and control of fractional‐order system for permanent magnet synchronous motor velocity servo system

This study presents fractional-order system modelling and control for a permanent magnet synchronous motor (PMSM) velocity servo system. Fractional-order model of the PMSM velocity servo system is obtained theoretically for an improved modelling precision. To identify the parameters of the proposed fractional-order model, an enhancement of the classic Levy identification method with weights is applied. In a real-time PMSM velocity servo plant, the fractional-order model is identified according to the experimental tests using the presented algorithm. The fact that the fractional model is more accurate than traditional integer-order model is substantiated using by the mean square error performance index. Two H ∞ stabilising output feedback controllers are designed for velocity servo using a simple scheme according to the identified fractional-order model and the traditional integer order one, respectively. The experimental test performance using these two designed H ∞ controllers is compared to demonstrate the advantage of the proposed fractional-order model of the PMSM velocity system.

Matlab Based Interactive Model of a Position Servo Drive

An interactive MATLAB based simulation tool is presented that may be used for verifying properties of several position control loops for electrical drives with a torque generator and position measurement by an incremental position sensor. The compared loops include cascade P-PI control with P controller in a position loop and PI controller in an underlying velocity loop, its filtered versions denoted as P-FPI and FP-FPI controls, and the solution with PD controller and disturbance observer (DO) using low pass filters in the disturbance observer and in the position feedback (DO-FPID). All controls may be supplemented by a feedforward to eliminate the error if a setpoint signal is continuous. As a default option the tool provides parameter tuning of all position controllers for a nearly equal integral of absolute error (IAE) of setpoint steps. Differences in the noise impact are highlighted by relative total variance of the input and output signals. The tool enables users an experimental way of discovering properties of particular loops. It exhibits high importance of appropriate filter design and shows that the solutions with the feedback filters may yield for both the nominal and uncertain situations the highest performance to noise impact (torque ripple) ratio.

Multi-pole modeling and simulation of an electro-hydraulic servo-system in an intelligent programming environment

AbstractThe paper presents composing of models and simulation of an electro-hydraulic servo-system, including hydraulic servo-drive with feedback regulator, electro-hydraulic servo-valve and constant pressure feeding system with variable displacement pump. For composing mathematical models of the fluid power system multi-pole models with different oriented causalities are used. Using multi-pole models allows describe models of required complexity for each component. Using a Java based intelligent programming environment CoCoViLa as a tool, enables one graphically describe multi-pole models of the system and perform simulations in a user-friendly manner. Solving large equation systems during simulations can be avoided. Models of four-way sliding spool throttling slot pairs describe open slot and overlapped slot characteristics of various causalities. For correcting the control signal to the electro-hydraulic servo-valve a non-linear differential regulator is used. An intelligent simulation environment CoCo...

English

In this paper, an FPGA model of RC servo and Stepper motor control system was built. This system consists of EP2C5T144C8 Cyclone II Mini Board, 9 grams micro servo motor, 28BYJ-48 Stepper Motor, ULN2003 motor driver. This system operates 3 functions parallelly, a simple binary count with the 3 LEDs on the board, from 0 to 7, controlling a RC servo, where the position is dependent on the value in the previous counter. The servo starts when the counter value goes from 000 to 001 for the first time. After counting from 0 to 7 for the first time, the servo goes to its initial position when the counter goes to 000 for all the time and controlling a Stepper motor, where the speed is dependent again on the previous counter. The proposed model is built using Verilog HDL, simulated using Modelsim Altera Starter Edition 10.1d and synthesized using Xilinx ISE 9.2i package, and will be implemented using Cyclone II FPGA Mini Board kit. Implementation and Simulation behavioral model results show that the proposed model satisfies the specified operational requirements. Keywords— Servo motor, Stepper motor, Motor Driver, RTL, Verilog

Improved dynamic model of electro- hydraulic servo and actuator system for steam turbine in power systems

Accuracy system model and its parameters are of great importance in stability and security evaluation or simulation for power systems. The electro-hydraulic servo and actuator is one of the most important components in the system. A mathematical model for the electro-hydraulic servo and actuator system developed on the working principle of each component has model parameters with clear physical meanings that can be obtained from field test data. The model is validated by data from four reheat turbines with different digital electro-hydraulic (DEH) control systems. Simulations show that the model agrees well with the test data when the servo cards are either proportional or proportional integral controllers. The results also show that the IEEE model parameters can be derived by this model.