Force Servo Research Articles

Design and Experimental Research of Movable Cable-Driven Lower Limb Rehabilitation Robot

Aiming at solving the problems of the existing lower limb rehabilitation robots on aspects of configuration limitations, human–machine compatibility, gravity compensation, and multimodal rehabilitation, a movable cable-driven lower limb rehabilitation robot (MCLR) is proposed in this paper, which can realize the gait training and walking training in passive mode, initiative mode, and assistive mode. First, the structure and working principle of MCLR is introduced. The traction type is further optimized. Second, the key control problems of the passive force servo system are analyzed in detail. In order to improve the loading accuracy and speed during the initiative training, the dynamic model of the cable-driven unit is established. Based on this model, an active force control strategy is proposed. Finally, the speed control strategy and the active force control strategy are studied experimentally. The experimental results show that the speed servo system has good tracking ability, which can meet the requirements of the passive rehabilitation. The active force control strategy can significantly improve the loading accuracy and the dynamic performance of the force servo system. The force servo system has good tracking ability in the normal rehabilitation frequency band, which can meet the requirements of the initiative rehabilitation.

Study on the compensation control of electro-hydraulic servo force loading in nonlinear variable load condition

Nonlinear variable load is one of the most important factors affecting the tracking performance and the robustness in electro-hydraulic servo force loading systems, which causes a great output dist...

The integral sliding mode control of a pneumatic force servo for the polishing process

The automation of the polishing process is essential to improve the production efficiency and the quality of the part surfaces. The control strategy, which involves the position/force control, is a big bottleneck for the automated polishing process. This paper focuses on the precise control of the pneumatic force in polishing. Firstly, a position/force decoupled polishing system is described, which consists of a tool-path control subsystem and a polishing force control subsystem based on a pneumatic force servo. Then, the dynamic model of the pneumatic force servo is identified by evaluating the system output while the input is provided by the Pseudo Random Binary Sequence (PRBS) signals. Based on this dynamic input-output model, a new integral sliding mode controller (ISMC), which is composed by equivalent control and switching control, is especially designed for the non-minimum phase system identified. The force control experiments show that the proposed controller is effective in suppressing the external disturbance of spindle rotation and model uncertainties due to the nonlinear characteristics of the pneumatic system; and the control accuracy of the polishing force is improved compared to the traditional PID controller and RST controller. Finally, the polishing experiment of a spherical surface with uniform material removal has been conducted and the polishing results show that the surface roughness greatly improved from 135.8 nm to 14.7 nm. This new integral sliding model control method is effective and has great potential application in the further industrial polishing force control.

Research on structure decoupling of passive electro-hydraulic force servo system

In order to study the strong force/position coupling problem of passive electro-hydraulic force servo system, taking the valve control swing motor of passive electro-hydraulic force servo system as...

A Novel Robust Constraint Force Servo Control for Under‐actuated Manipulator Systems: Fuzzy and Optimal

AbstractWe consider the control design for under‐actuated manipulator systems. The task is to drive the system to be close to a prescribed constraint. The system contains uncertainty. It is bounded where the bounding information is prescribed by a fuzzy set (e.g., the bound is close to 1). The initial condition is also prescribed by a fuzzy set. A class of robust control is proposed, which guarantees a deterministic performance. On top of that, the choice of a control design parameter is cast into a fuzzy‐theoretic setting. A performance index, consisting of accumulated fuzzy‐based system performance and control cost, is proposed. The optimal control design parameters, which minimize the performance index, can be obtained by solving two algebraic quartic (fourth‐order) equations. As a result, the control design problem, which addresses both fuzzy and optimal characteristics, is completely solved.

Modeling and Simulation of Force Control System of Triaxial Testing Machine Based on AMESim/Simulink

A servo force control system based on iterative learning control algorithm is proposed for the characteristics of nonlinear, strong cross coupling and parameter uncertainty of triaxial loading hydraulic servo system. Through the mathematical modeling of hydraulic servo force control system to determine the control parameters of the iterative algorithm, finally, the AMESim/Simulink is used to model and combine the simulation. The simulation results show that the control method can effectively improve the control accuracy of the three-axis loading servo-control system and improve the response speed of the system. The simulation results show that the control method can effectively improve the control accuracy of the three-axis loading servo-control system and improve the response speed of the system.

Improved RBF Neural Network PID Control Strategy and Its Application in Pneumatic Force Servo System

Improved RBF Neural Network PID Control Strategy and Its Application in Pneumatic Force Servo System

Research on Electro-Hydraulic Force Servo Control System Based on Specialist PID Control Strategy

There is flexibility load in the electro-hydraulic force servo control system researched in this paper, and it results in that there is a lower oscillation frequency secondary differential element in radical of the transmit function of the system. The flexibility load and the secondary differential element seriously impact the bandwidth of the system and let the bandwidth rise difficultly, and that the flexibility load and the secondary differential element make the system oscillation even instability easily. Aiming at this special characteristic and the smaller system gain characteristic of the electrohydraulic force servo control system, the specialist PID control theory applied to the electro-hydraulic force servo control system which is the typical nonlinear system. The mathematic model of the system is built and the simulation and the experiment research is finished in the work of this paper, at the same time, the author of this paper compares the control result of the new controller designed according to the specialist PID control theory with the control result of traditional PID controller. The simulation and the experiment results indicate that the new controller designed according to the specialist PID control theory not only enlarge the bandwidth of system, improve the accuracy, reduce control error, but also accelerate the response speed obviously, increase the dynamic property of the system.

Real-time tracking control of electro-hydraulic force servo systems using offline feedback control and adaptive control

This paper focuses on an application of an electro-hydraulic force tracking controller combined with an offline designed feedback controller (ODFC) and an online adaptive compensator in order to improve force tracking performance of an electro-hydraulic force servo system (EHFS). A proportional-integral controller has been employed and a parameter-based force closed-loop transfer function of the EHFS is identified by a continuous system identification algorithm. By taking the identified system model as a nominal plant model, an H∞ offline design method is employed to establish an optimized feedback controller with consideration of the performance, control efforts, and robustness of the EHFS. In order to overcome the disadvantage of the offline designed controller and cope with the varying dynamics of the EHFS, an online adaptive compensator with a normalized least-mean-square algorithm is cascaded to the force closed-loop system of the EHFS compensated by the ODFC. Some comparative experiments are carried out on a real-time EHFS using an xPC rapid prototype technology, and the proposed controller yields a better force tracking performance improvement.

Compared with PI, Fuzzy-PI and PSO-PI Controllers of Robotic Grinding Force Servo System

By grinding process, when an industrial robot is used to finish a curved surface, both feed movement and contact force must controlled at the similar time in order that the grinding tool would machine the work-piece at the right position in right posture with required force. A passive wrist system is advanced, in this paper, to conform the shape of the machining propeller by altering its posture along with the surface. The proportional-integral (PI) controller, due to its simplicity, robustness, and affordable price, is extremely often used in practical applications, but it is effective for linear systems, as well as, the challenging task is to find its optimal gains. If the processes involved higher order and time delay systems, many intelligent controllers were appeared. In this paper, to cope with nonlinearities, improve the controller parameters and at the same time modeling uncertainties of grinding marine propeller surface, a PI torque controller is proposed such that its optimal gains are derived via a modern systems based on fuzzy logic theory and particle swarm optimization algorithm which are used to solve various engineering problems. Grinding force is controlled under Fuzzy-PI controller which is being assembled and compared with a PSO-PI controller to obtain which controller that provides grinding with higher quality. The compared controllers have been optimized together with the parameters of the Two-Phase Hybrid Stepping Motor. The suggested fuzzy rule function and PSO algorithm improve the response of the controlled system and searches a high-quality solution impressively. Simulation and comparison results are presented and that the proposed control systems are coping well with nonlinearities and uncertainties while find PI control parameter set effectively, the PSO-PI controller has a better control performance with improved step response for robotic grinding force servo system. These control methods was simulated using MATLAB/SIMULINK.

Compared with PI, Fuzzy-PI and PSO-PI Controllers of Robotic Grinding Force Servo System

<p>By grinding process, when an industrial robot is used to finish a curved surface, both feed movement and contact force must controlled at the similar time in order that the grinding tool would machine the work-piece at the right position in right posture with required force. A passive wrist system is advanced, in this paper, to conform the shape of the machining propeller by altering its posture along with the surface. The proportional-integral (PI) controller, due to its simplicity, robustness, and affordable price, is extremely often used in practical applications, but it is effective for linear systems, as well as, the challenging task is to find its optimal gains. If the processes involved higher order and time delay systems, many intelligent controllers were appeared. In this paper, to cope with nonlinearities, improve the controller parameters and at the same time modeling uncertainties of grinding marine propeller surface, a PI torque controller is proposed such that its optimal gains are derived via a modern systems based on fuzzy logic theory and particle swarm optimization algorithm which are used to solve various engineering problems. Grinding force is controlled under Fuzzy-PI controller which is being assembled and compared with a PSO-PI controller to obtain which controller that provides grinding with higher quality. The compared controllers have been optimized together with the parameters of the Two-Phase Hybrid Stepping Motor. The suggested fuzzy rule function and PSO algorithm improve the response of the controlled system and searches a high-quality solution impressively. Simulation and comparison results are presented and that the proposed control systems are coping well with nonlinearities and uncertainties while find PI control parameter set effectively, the PSO-PI controller has a better control performance with improved step response for robotic grinding force servo system. These control methods was simulated using MATLAB/SIMULINK.</p>

PSO_PI Controller of Robotic Grinding Force Servo System

When an industrial robot is used to grind a curved surface ,as marine propeller surface, contact force and feed movement must controlled together at the similar time in order that the grinding tool would machine the work-piece, with required force, at the right position in right posture. A passive wrist system is advanced, in this paper, to conform the shape of the machining propeller by altering its posture along with the surface. Grinding force is controlled under a simple new PSO-PI controller at a steady value in the normal direction of the mentioned machining point by multi-point machining, while the grinding tool moving along the curved surface of the propeller. It means that the model of the passive wrist system and the surroundings could be used in force controlling when robots grind marine propeller surface by a grinding tool with multi-point machining. PSO_PI controller policy is being assembled and compared with a PI controller to obtain a controller that provides grinding with higher quality. The compared controllers have been optimized together with the parameters of the Two-Phase Hybrid Stepping Motor. The particle swarm optimization (PSO) method was selected from several methods to optimize of Proportional-Integral controller parameters in order to give better performance with improved step response for robotic grinding force servo system and overshoot are reduced. This control method was simulated using MATLAB/SIMULINK.

PSO_PI Controller of Robotic Grinding Force Servo System

When an industrial robot is used to grind a curved surface ,as marine propeller surface, contact force and feed movement must controlled together at the similar time in order that the grinding tool would machine the work-piece, with required force, at the right position in right posture. A passive wrist system is advanced, in this paper, to conform the shape of the machining propeller by altering its posture along with the surface. Grinding force is controlled under a simple new PSO-PI controller at a steady value in the normal direction of the mentioned machining point by multi-point machining, while the grinding tool moving along the curved surface of the propeller. It means that the model of the passive wrist system and the surroundings could be used in force controlling when robots grind marine propeller surface by a grinding tool with multi-point machining. PSO_PI controller policy is being assembled and compared with a PI controller to obtain a controller that provides grinding with higher quality. The compared controllers have been optimized together with the parameters of the Two-Phase Hybrid Stepping Motor. The particle swarm optimization (PSO) method was selected from several methods to optimize of Proportional-Integral controller parameters in order to give better performance with improved step response for robotic grinding force servo system and overshoot are reduced. This control method was simulated using MATLAB/SIMULINK.

Fuzzy-PID Controller of robotic grinding force servo system

When a robot is used to grind or finish a curved surface ,as marine propeller surface, both contact force and feed movement must controlled at the similar time in order that the grinding tool would machine the work-piece, with required force, at the right position in right posture. A compliant wrist system is advanced, in this paper, to conform the shape of the machining propeller by altering its posture along with the surface. Grinding force is controlled under a simple new Fuzzy-PID controller with five input variables which assembled and compared with an antecedently used PID controller. The aim of defining the rules and its optimization are to achieve a controller that provides grinding with higher quality. Both the controllers PID and Fuzzy-PID have been optimized together with the parameters of the Two-Phase Hybrid Stepping Motor The Fuzzy-PID controller policy at a steady value in the normal direction of the mentioned machining point by multi-point machining, while the grinding tool moving along the curved surface of the propeller. It means that the model of the compliant wrist system and the surroundings could be used in force controlling when robots grind marine propeller surface by a grinding tool with multi-point machining. DOI: http://dx.doi.org/10.11591/telkomnika.v15i1.8051

Improving manufacturing of aeronautical parts with an enhanced industrial Robotised Fibre Placement Cell using an external force-vision scheme

Composite materials are increasingly used in the demanding field of aeronautics. To meet this growing need, the company Coriolis Composites has developed an automated fibre placement device already on the market. This process uses an industrial manipulator robot. This fibre placement task requires a compacting strength adapted to the material used. For the robot, the reference trajectories in position of each tape are prescribed off-line. However, accuracy problems of tape placement appear when off-line programmed robot trajectories. The proposed approach to address the accuracy problem and the manufacturing constraints is an interactive manufacturing scheme based on exteroceptive sensor loops. This paper shows an interactive manufacturing approach based on force servoing to control the compacting strength and on visual servoing to control the lateral position of the tape in order to improve the fibre placement accuracy and then the quality of manufactured parts.

Adaptive position tracking control of electro-hydraulic six-degree-of-freedom driving simulator subject to perturbation

In this paper, a new Lyapunov-based adaptive control scheme for the position tracking of an electro-hydraulic Stewart–Gough platform type six-degree-of-freedom (DOF) driving simulator is proposed. The kinematics and the dynamics of both the moving platform and the hydraulic actuator are first derived, and the linearized dynamic equation of the moving platform is developed for the controller design. Two control loops are employed, in which the platform controller is in the outer loop and the actuator controllers are in the inner loop. In the platform controller, the compound proportional-differential (PD) feedback and adaptive compensation controller is designed. The PD part is used to create the principal control signal, and the adaptive part is used to compensate for the parameter uncertainty and external disturbance. To suppose that the upper bound of the perturbation is known, a gradient descent method-based adaptive law is developed for parameter estimation. For each actuator controller a servo force control scheme is designed to ensure the actuator to accurately track the desired force output by the platform controller. All the controllers are designed together based on the Lyapunov method to guarantee the stability of the whole system. Numerical simulation on a six-DOF simulator shows that the proposed control scheme has better tracking performance than its non-adaptive counterpart.

Force feedback coupling with dynamics for physical simulation of product assembly and operation performance

Most existing force feedback methods are still difficult to meet the requirements of real-time force calculation in virtual assembly and operation with complex objects. In addition, there is often an assumption that the controlled objects are completely free and the target object is only completely fixed or free, thus, the dynamics of the kinematic chain where the controlled objects are located are neglected during the physical simulation of the product manipulation with force feedback interaction. This paper proposes a physical simulation method of product assembly and operation manipulation based on statistically learned contact force prediction model and the coupling of force feedback and dynamics. In the proposed method, based on hidden Markov model (HMM) and local weighting learning (LWL), contact force prediction model is constructed, which can estimate the contact force in real time during interaction. Based on computational load balance model, the computing resources are dynamically assigned and the dynamics integral step is optimized. In addition, smoothing process is performed to the force feedback on the synchronization points. Consequently, we can solve the coupling and synchronization problems of high-frequency feedback force servo, low-frequency dynamics solver servo and scene rendering servo, and realize highly stable and accurate force feedback in the physical simulation of product assembly and operation manipulation. This research proposes a physical simulation method of product assembly and operation manipulation.

Research on Electro-Hydraulic Force Servo System Based on Neural Network and Fuzzy Intelligent Control Strategy

Research on Electro-Hydraulic Force Servo System Based on Neural Network and Fuzzy Intelligent Control Strategy

PRACTICAL FRICTION MODELS AND FRICTION COMPENSATION IN HIGH-PRECISION ELECTRO-HYDRAULIC SERVO FORCE CONTROL SYSTEMS

Nonlinear friction is the main factor in the electro-hydraulic servo force control system. It causes steady-state and tracking errors that are difficult to eliminate during static and dynamic loading. In recent years, many studies have been done to reduce or eliminate the influence of the friction in the control system. This article discusses an electro-hydraulic servo force control system to complete simulation experiments in the laboratory. According to friction theory, the effect of friction near the zero-velocity point that appeared twice within a cycle during the test would be very obvious, which distorts the waveform and decreases the control accuracy. Due to the special purpose of the electro-hydraulic servo force control system, a practical friction compensation method has been introduced in this article. The friction static friction model, dynamic friction model, and identification methods are discussed in detail. The experimental results show that this practical friction compensation method can significantly reduce the influence of the nonlinear friction and improve control accuracy in the high-precision electro-hydraulic servo force control system.

Design and Simulation Study of a Certain Landing Gear Loading Simulation System

The landing gear ground loading tests is a vital part before flight. As the motion of landing gear is three-dimensional motion,the traditional loading method cannot effectively simulate the pneumatic load on the ground. In order to simulate the load in the process of retraction/extension, a loading simulation system is proposed, including retractile system, position follow-up system and force servo loading system. This paper analyzes retraction/extension mechanism of the landing gear and builds up its mathematical model. A co-simulation model is developed in which the hydraulic system model and control system are built in software AMESim, the mechanical system of test platform model is built in software ADAMS. The results of the simulation confirm that the loading simulation system is feasible and provide the basis for building hardware platform.