Force Servo Control Research Articles

Research on sports aided teaching and training decision system oriented to deep convolutional neural network

Aiming at the construction of the decision-making system for sports-assisted teaching and training, this article first gives a deep convolutional neural network model for sports-assisted teaching and training decision-making. Subsequently, In order to meet the needs of athletes to assist in physical exercise, a squat training robot is built using a self-developed modular flexible cable drive unit, and its control system is designed to assist athletes in squatting training in sports. First, the human squat training mechanism is analyzed, and the overall structure of the robot is determined; second, the robot force servo control strategy is designed, including the flexible cable traction force planning link, the lateral force compensation link and the establishment of a single flexible cable passive force controller; In order to verify the effect of robot training, a single flexible cable force control experiment and a man-machine squat training experiment were carried out. In the single flexible cable force control experiment, the suppression effect of excess force reached more than 50%. In the squat experiment under 200 N, the standard deviation of the system loading force is 7.52 N, and the dynamic accuracy is above 90.2%. Experimental results show that the robot has a reasonable configuration, small footprint, stable control system, high loading accuracy, and can assist in squat training in physical education.

Control strategy and experimental research of a cable-driven lower limb rehabilitation robot

This paper aims to solve the problems of the existing limbs rehabilitation robots in terms of configuration limitations, human-machine compatibility, multimodal rehabilitation training. In addition, the control method of the cable tension of cable drive unit (CDU) loading system is studied to improve loading accuracy of cable tension and safety of the rehabilitation training robot. The novelty of this work is to propose a compound correction controller that can not only ensure the tracking accuracy of the cable-driven lower limb rehabilitation robot (CDLR) but also effectively improve the force loading accuracy of the cable tension force. Hence, this paper proposes a CDLR that can realize the active training mode, passive training mode, and assistive training mode. Firstly, the structure and working principle of CDLR is introduced. The dynamic model of the CDU loading system is established and the frequency characteristic of the CDU loading system is analyzed. In order to improve the loading accuracy and response speed of the CDU loading system, a compound correction controller is designed based on the frequency characteristics of the CDU loading system. Finally, the active force servo control experiment and the passive force servo control experiment of the CDU loading system are carried out on the experimental platform. The experimental results show that the compound correction control strategy can meet the requirements of lower limb rehabilitation training in the active force servo control experiment; the compound correction control strategy can significantly improve the loading precision and dynamic performance of the system in the passive force servo control experiment. That is, the compound correction control strategy can meet the requirements of lower limb rehabilitation training. The results provide a basis for the whole robot experiment and human-machine experiments and improve the stability of the CDLR system and patient safety.

Improved Beetle Antennae Search Algorithm-Based Lévy Flight for Tuning of PID Controller in Force Control System

To enhance the anti-interference capability of an electrohydraulic force servo control system and increase the efficiency of the PID controller, this paper proposes a LBAS-PID controller. In LBAS, the random step created by the Lévy flight trajectory was used in the original algorithm to enhance the diversity of the population and convergence speed. In the force servo control system, LBAS-PID can enhance the performance of the system. First, the basic mathematical model of an electrohydraulic force servo control system was built based on theoretical analysis. The transfer function model was obtained by identifying the system parameters. Second, the introduced Lévy flight beetle antennae search algorithm was introduced and applied to ten benchmark functions, and the results were compared with those of other algorithms. Then, the proposed algorithm was applied in the PID controller to tune PID parameters in the force servo control system. To comprehensively evaluate performances of an electrohydraulic force servo control system that is controlled by the LBAS-PID controller, the frequency response analysis and temporal response analysis were obtained. The numerical analysis results indicate that an electrohydraulic force servo control system with an LBAS-PID controller could substantially increase the control characteristics of the system and restrain the external disturbances when different interference signals are examined.

Passive force control of multimodal astronaut training robot

For the purpose of solving the problem of astronaut training in weightlessness environment, this article proposes a multimodal astronaut training robot to enable astronauts to perform running, bench press and deep squat training in the weightless environment, so as to help them mitigate the adverse effects brought by the space adaptation syndrome. Taking the modularized wire driving unit as the research object, the dynamic model of the passive force servo system was established; and the passive force control strategy was designed. The experimental results show that the system is of good stability, high steady-state accuracy, and excellent dynamic quality after correction. When the given signal frequency is 10 Hz, the system phase lag is about 9°, and the loading error is about 5%. The passive force servo control strategy can effectively reduce the surplus force. When the speed disturbance frequency of carrying unit is within 3 Hz, the elimination rate of the surplus force can reach 90%.

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.

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.

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.

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.

Research on Electro-Hydraulic Force Servo Control System Based on Adaptive Neural Network Control Strategy

It is unchangeable fact that there is great stiffness spring flexible load in electro-hydraulic force servo control system, and there is low oscillation frequency second order differential link in the numerator of the transfer function. On the other hand, the frequency response ability of the system is influenced badly from the link and the system may oscillate easily even is instability. Aiming at this special performance of the electro-hydraulic force servo control system and its small open loop gain characteristic, the adaptive neural network control strategy is adopted to the controller of the electro-hydraulic force servo control system this special performance system in order to improve the dynamic performance of the system. The model of the system with the adaptive neural network control strategy is built and the simulation and experiment study is done. Comparing the control result of the controller with the adaptive neural network control strategy to the control result of the controller with the traditional PID, and from the results of simulation and experiment, we can know that the mathematic model of the electro-hydraulic force control system controlled by the adaptive neural network control strategy is correct, and we can find that the controller with the new designed control strategy can not only increase the frequency response ability of system, but also improve the precision of system, and the controller can quicken the response ability of the system obviously.

Study and Application of a Slide Mode Control on Pneumatic Force Servo System

In this paper, a sliding mode control approach combined with the boundary saturation function approach is put forward and used in a pneumatic force servo system to achieve an exact force control. First, a comparatively accurate model of the system is obtained by using the system identification approach and an analysis is made on the time-varying nature of the model. Then, it is designed by use of the boundary saturation approach, thus overcoming the system instability caused by the non-linearity of the proportional pressure valve and the change of the temperature inside the air cylinder. Finally, the performance of the pneumatic force servo control system is simulated and a comparison is made with the PID control. Results show the feasibility and effectiveness of the approach.

Hybrid Force/Position Control Hardware System Design and Force Servo Control Realization

The hardware control system of the 5-UPS/PRPU PMT (parallel machine tool) with redundant actuation was reconstructed to realize its hybrid force/position control, which was based on the primary “IPC+PMAC motion controller” system mode. Meanwhile, more perfect open type PMT control platform was constructed. Visual Basic language was used to realize the force servo control of the redundant limb and the relevant experiment was completed in the primary CNC system, combining with the PAMC motion controller library function. The results show that the force servo control strategy is exact and the newly designed hardware control system is effective, these results also provide feasible hardware basis and control method to realize the hybrid force/position control.

Unified software development approach for the safety-critical ITER maintenance devices

The RH devices used for ITER divertor maintenance are movers or manipulators composed of electro-hydraulic and electrical actuators. Such devices are CMM, CTM and WHMAN to assist CMM and CTM. These devices execute complex and safety-critical operations while supporting ITER reactor elements weighting several tons. Despite the differences in the load capacity and functionality, the control system of these devices can be categorized as position servo control or force servo control. In this paper we propose the use of unified software development approach currently developed and demonstrated at the DTP2. This new approach takes into account the ITER RH requirements for all maintenance devices, not only the water-hydraulic maintenance devices. The need for extensive software verification and validation utilizing international standards for safety-critical systems is addressed. This applies both to control software architecture and user interface design. In principle, we propose that all ITER maintenance devices are developed and tested with the common software architecture and user interface. This makes it possible to reuse generic software modules that are well documented and tested, resulting decreased verification and validation period and development cost. Utilising this approach also improves reliability and safety of the maintenance operations.

Design and implementation of force and position control with anti-windup conditioned transfer compensation

This paper investigates the design and implementation of a force and position servo control system where non-linearities are encountered due to constraint on the torque signal to the motor drive, and switching between position and force controllers. The so-called two-step design paradigm is employed, whereby the velocity, position and force controllers are designed first ignoring control input non-linearities, and then anti-windup and conditioned transfer compensators are added using the Hanus conditioning technique. Both linear position and force controllers are designed using the H∞ loop shaping design procedure, and the H∞ controllers are found such that the Hanus conditioning technique for anti-windup conditioned transfer compensation can be applied. The overall controller is derived and presented in the state space framework, and its performance is evaluated in real time on an experimental set-up using a commercial digital signal processor.