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In order to ensure good dynamic characteristics, servo valve is usually adopted as the drive part of Stewart manipulator which causes huge power consumption, while direct drive electro-hydraulic servo system has the advantages of energy saving, simple structure, convenient installation, and low failure rate. But its dynamic characteristics are so p...
Contexts in source publication
Context 1
... basic schematic diagram of the direct drive hydraulic system above is shown in Figure 4. Plummer proposed a direct drive hydraulic system for Stewart manipulator [19]. ...
Context 2
... basic schematic diagram of the direct drive hydraulic system above is shown in Figure 4. ...
Context 3
... basic schematic diagram of the direct drive hydraulic system above is shown in Figure 4. For direct drive system, rotation speed of the servo motor is usually selected as the control input. ...
Citations
... There are many nonlinear factors in the electrohydraulic servo system [23], including the dead zone of the servo valve, hysteresis, the Coulomb friction of the hydraulic actuator, etc. The main consideration in this article is the nonlinear effect of the flow equation of the servo valve. ...
In this paper, an automated umbilical system based on a 6-dof (degree of freedom) hydraulic parallel mechanism is proposed to automate the rocket propellant loading process. The mechanical structure, vision acquisition algorithm, and control algorithm used in the system are described in detail in the paper. To address the fluid nonlinearity problem of the hydraulic drive system, nonlinear compensation and three-state feedback control are used in the paper to enhance the performance of the hydraulic system. For the problem of force tracking during the docking process between the umbilical system and the rocket, an adaptive impedance control algorithm based on the online environmental parameter estimation is proposed in the paper, which effectively reduces the contact force during the docking process. The dynamic tracking and docking experiments indicate that this automated umbilical system features rapid reaction speed, high measurement precision, and good flexibility, which can be used to realize the auto-mating and following task for the propellant loading robot in a hazardous environment.
... Zhang C. showed that DPF remains welcome to suppress resonances in electro-hydraulic systems [12]. Nevertheless, with digital signal processors indispensable nowadays, a notch filter is preferred and proved effective [13][14][15][16], especially attractive in aerospace uses where hardware reduction means higher reliability. ...
It is difficult to describe precisely, and thus control satisfactorily, the dynamics of an electro-hydraulic actuator to drive a high thrust liquid launcher engine, whose structural resonant frequency is usually low due to its heavy inertia and complicated mass distribution, let alone one to drive a heavy kerolox engine with high-order dynamics. By transforming classic control block diagrams, a baseline two-mass-two-spring load model and a normalized actuator-engine system model were developed for understanding the basic physics and methodology, where a fourth-order transfer function is used to model the multi-resonance-frequency engine body outside of the rod position loop, another fourth-order transfer function with two pairs of conjugated zeros and poles to represent the composite hydro-mechanical resonance effect in the closed rod position loop. A sixth-order model was thereafter proposed for even higher dynamics. The model parameters were identified and optimized by a full factor search approach. To meet the stringent specification of static and dynamic performances, it was demonstrated that a notch filter network combined with other controllers is needed since the traditional dynamic pressure feedback (DPF) is difficult to handle the high-order dynamics. The approach has been validated by simulation, experiments and successful flights. The models, analysis, data and insights were elaborated.
... The structure and the direct drive hydraulic system of the direct drive 6-DOF parallel mechanism in [21] are shown in Figure 1. The motion of the upper platform which is usually made of steel is generated by six symmetrical direct drive legs. ...
... Usually, smooth joints which can eliminate the effects of the joint friction on its dynamics characteristics are often adopted in the parallel mechanism, so the load of the parallel mechanism is mainly composed of the inertia load. Since the hydraulic system of each leg of the direct drive 6-DOF parallel mechanism is the same, and the complete coupled transfer function with the torque mode can be transformed into six independent single DOF control systems with modal space coordinate transformation, which are quite similar to that of a single DOF direct drive hydraulic system with inertia load [21], the hydraulic system of the direct drive 6-DOF parallel mechanism can be simplified to a single DOF hydraulic system which costs much less and the study of this paper can also be carried out with the simplified system, which should be exactly the same with the hydraulic system of each leg of the direct drive 6-DOF parallel mechanism. It is worth noting that the hydraulic and electric components of the single DOF hydraulic system should be selected according to the requirements of the direct drive 6-DOF parallel mechanism. ...
... Since both Equation (3) and Equation (4) apply to the speed mode and the torque mode, the parameters of the second-order element with the speed mode and the dynamic second-order element with the torque mode are quite similar. According to [21], both proportion differentiation (PD) control strategy and dynamic pressure feedback (DPF) control strategy which are designed to increase the bandwidth of the direct drive 6-DOF parallel mechanism should also be adopted to improve the dynamic performances of the direct drive hydraulic system in Figure 2 with the torque mode, experimental verification is also carried out. ...
The torque mode is more suitable for the direct drive 6 degree of freedom (6-DOF) parallel mechanism than the speed mode that both dynamic coupling and current coupling among motors are easily solved, but its key parameters and dynamic characteristics have never been studied, which are important and are the goals of this paper. First the hydraulic system of the direct drive 6-DOF parallel mechanism is simplified. Then the transfer function of the direct drive hydraulic system with the torque mode is deduced together with that of the speed mode. Finally, comparative experiments are conducted. Results show that the dynamic characteristics of the system with the torque mode which are generally worse than those with the speed mode, are mainly determined by the parameters of the motor-pump second-order element of the transfer function composed of two under-damped second-order elements, proportion differentiation (PD) control strategy and dynamic pressure feedback (DPF) control strategy are useful for the system with the torque mode, but practical and effective methods are still needed.
With the rapid development of the manufacturing industry, industrial automation equipment represented by computer numerical control (CNC) machine tools has put forward higher and higher requirements for the machining accuracy of parts. Compared with the multi-axis serial platform solution, the parallel platform solution is theoretically more suitable for high-precision machining equipment. There are many parallel platform solutions, but not one can provide a common physical platform to test the effectiveness of a variety of control algorithms. To achieve the goals, this paper is based on the Stewart six degrees of freedom parallel platform, and it mainly studies the platform construction. This study completed the mechanical structure design of the parallel platform. Based on the microprogrammed control unit (MCU) + pre-driver chip + three-phase full bridge solution, we have completed the circuit design of the motor driver. We wrote the program of MCU to drive six parallel robotic arms as well as the program of the parallel platform control center on the PC, and we completed the system joint debugging. The closed-loop control effect of the parallel platform workspace pose is realized.
When optimizing hydraulic systems, various algorithms are used, which are based on the control quality indicators selected as target functions. This is why there is a need to automate the calculation of these indicators. The article considers the main indicators of the quality of the transition process, a mathematical model of the LUDV hydraulic system is compiled and its calculation is performed in two mathematical modeling packages in order to confirm the accuracy of the initial data. An algorithm for determining the main quality indicators of the transition process has been developed, which makes it possible to simplify and speed up the optimization process of the considered LUDV-hydraulic system.
