Open-loop Control Experiments Research Articles

Vibration characteristics control of hybrid radial gas foil bearing-rotor system: Simulation and experiment

Currently, tiny, high-speed rotating machines frequently employ air foil bearings. Air is employed as the working medium, however, when the rotor speed is high, the rigidity of the air film is insufficient, which restricts the usage of air foil bearings. This study utilizes the external gas supply method of hydrostatic gas bearings to strengthen the air film stiffness of air foil bearings. The original air foil bearings are combined with external gas supply piping to create the hybrid gas foil bearing(HGFB), which may be utilized to increase the air film support stiffness of the bearings through the external gas supply. Additionally, by altering the gas supply pressure, this bearing may be used to actively manage the vibration characteristics of the shaft system, allowing the bearing performance to be adjusted to changing operating conditions. The static and dynamic properties of the HGFB with a 24 mm diameter are solved in this study using Newton's iterative approach and the finite difference method. The bearing-rotor system is modeled using this information. An Analysis is done on the impact of various air supply pressures and throttle hole widths on bearing performance and vibration characteristics of the shaft system. In this article, the vibration parameters of the bearing-rotor system are tested using an open-loop control test. The open-loop control experiment on the vibration response of the bearing-rotor system is performed using HGFBs with orifice sizes of 0 mm, 0.2 mm, 0.4 mm, 0.6 mm, 0.8 mm, and 1.0 mm. The experimental results confirm the accuracy of the simulation results. Correspondingly, this paper conducted closed-loop control comparison experiments on the vibration properties of the bearing-rotor system using the PID control method and the fuzzy PID control method in succession. It then evaluated the control effect of the two control strategies on the vibration of the bearing-rotor system and managed to improve the conventional PID control method used for gas bearings.

Fabrication of three-lobed magnetic microrobots for cell transportation.

Mobile microrobots have the potential to transform medical treatments based on therapeutic delivery. Specifically, microrobots are promising candidates for cell transportation in cell-based therapies. Despite recent progress in cellular manipulation by microrobots, there is a significant need to design and fabricate microrobots to advance the field further. In this work, we present a facile approach to manufacturing three-lobed microrobots by a bench-top procedure. The microrobots are actuated by a harmless magnetic field which makes them biofriendly. Chemically, these microrobots are made of organosilica. The microrobots showed equally good control in both the open-loop and closed-loop settings. The three-lobed microrobots have two modes of motion during the open-loop control experiments. We employed these two modes for single-cell transportation. Our results show that the three-lobed microbots are very promising for cell transportation in a fluid.

Design and modeling of a hydraulic soft actuator with three degrees of freedom

This paper focuses on the design and modeling of a hydraulic soft actuator which can perform space motion with multiple degrees of freedom (DOF). The cylinder soft actuator made of elastomer has three fiber-reinforced hydraulic chambers distributed symmetrically. By controlling the pressure vector in the chambers, the motion of the soft actuator can be expressed by three independent variables including axial elongation, bending angle, and azimuth angle. This paper firstly presents the actuation principle, structural design, and fabrication method of the soft actuator. Secondly, the relationship between the input pressure and the axial length of the chamber is derived by taking the nonlinear deformation behavior of the elastomer into account, which is seldom considered in the state of the art. Thirdly, the kinematics of the soft actuator is modeled to predict the coordinates of its tip position with the piecewise constant-curvature (PCC) assumption. Finally, an experimental platform is set up and a series of experiments are implemented to identify some parameters which are difficult to be quantified analytically as well as to validate the developed model. The results show that the measured data are in good accordance with the predicted data. In addition, a model-based open-loop control experiment is carried out to realize the path following.

Error field feedback control system in the Keda Torus eXperiment and open loop control experiment

A feedback control system has been designed for the Keda Torus eXperiment device to achieve the following goals: (a) suppression of the error field at the poloidal gap, (b) three-dimensional plasma stability control, and (c) improvement of plasma discharge quality. The system consists of a boundary electromagnetic probe array, a field-programmable gate array, a linear power amplifier, and an active control coil array. The system adopts a compound control method that includes both active and passive control methods. To control the plasma, an active control coil array is used to generate a localized radial magnetic field as needed at two poloidal gaps of the device. In the open-loop control experiment, the active control coils near the poloidal gaps reduced the original error field and thus increased the plasma discharge current amplitude by 50% and effectively extended the plasma discharge duration.

Design and verification of model predictive control for micro-turboshaft engine

In this article, a nonlinear model predictive control algorithm for a micro-turboshaft engine is designed. The control effect is verified by a bench test. First, a micro-turboshaft engine test bench is built, and the open-loop control experiment was carried out on it. Based on experiment data, a linear parameter varying prediction model is established. Then, by online rolling optimization based on multistep output prediction, together with feedback correction, a nonlinear model predictive control algorithm is obtained. The influence of algorithm parameters on the control effect is studied, and reasonable prediction period M, control period N, and control coefficient R are designed. Finally, the application of nonlinear model predictive control in micro-turboshaft engine is verified by bench test. The results show that with the changing of pitch angle, nonlinear model predictive control algorithm has a faster adjustment speed and smaller overshoot, compared with the conventional cascade proportional–integral control with feedforward. It is proofed that nonlinear model predictive control can be applied to a real turboshaft engine and has a better control effect.

Closed-loop enhancement of jet mixing with extremum-seeking and physics-based strategies

The closed-loop control of a turbulent round air jet is experimentally investigated based on two unsteady minijets, with a view to enhancing jet mixing. The two minijets are placed at diametrically opposite locations upstream of the nozzle exit. The open-loop control experiments are first performed. Given the mass flow rate ratio C m of the minijets to that of the main jet, the decay rate $$\overline{K}$$ of jet centerline mean velocity exhibits a maximum at the frequency ratio f e/f 0 ≈ 1.0, where f e and f 0 are the excitation frequency of minijets and the preferred mode frequency of the natural main jet, respectively. An extremum-seeking feedback control has been developed to achieve autonomously the optimal control performance. It has been found that, given C m, this closed-loop control technique may obtain automatically and rapidly the optimal value of f e and the desired or maximum $$\overline{K}$$ , as achieved in the open-loop control. This control technique is robust and adaptable when the Reynolds number and initial excitation frequency are changed separately. A flow-physics-based feedback control strategy has also been investigated, which could achieve the optimal control performance automatically with a shorter convergence time than the extremum-seeking control, not robust though.

Experimental Studies on the Fuel Control Method of the Scramjet Combustor

The fuel control method of the liquid kerosenefueled scramjet combustor was investigated experimentally in this article. The primary goal was to experimentally demonstrate the possibility of using the closed-loop control with a combustor wall pressure feedback in the scramjet combustor. The open-loop control and the closed-loop control experiment were investigated by using the direct-connected test facility of Northwestern Polytechnical University. The typical flow conditions at the combustor entrance were: Mach number Ma = 2.0, totaltemperature Tt ≈ 880 K and total-pressure Pt = 700 ~ 800 kPa, which corresponded to a flight condition with Mach number 4.0. The monotone relationship between the wall pressure and the engine thrust was experimentally demonstrated by the open-loop control experiments. The closed-loop control experiments demonstrated that it was feasible to use wall pressure or pressure ratio as the feedback parameter in the closed-loop control, and the results indicate that it can precise control the fuel applying and shows a good performance.

Compensator design for hysteresis of a stacked PZT actuator using a congruency-based hysteresis model

This paper proposes a rate-independent hysteresis compensator for a stacked PZT (lead zirconate titanate) actuator. From a congruency-based hysteresis (CBH) model which is derived from the inherent properties of this actuator, especially the congruency, a feedforward compensator associated with it is developed. The formulation of the proposed compensator is based on an assumption that the inverse operator also possesses the same properties as the CBH model does. This implies that the compensator also possesses properties such as the wiped-out loop closing between the consecutive control points and congruency. Consequently, the expressions for the compensator can be conducted by exploiting the equations for the CBH model in two cases of monotonic increase and monotonic decrease of input excitation. In order to assess the performance of the compensator, several experiments in both open-loop and closed-loop controls are undertaken. In the open-loop control experiment, the performance of the feedforward compensator using the CBH model is compared with the classical Preisach model-based one in three cases of reference waveforms. In the closed-loop control experiment, the proposed compensator is incorporated into a PID (proportional-integral-derivative) control system and the performance of this integrated system is then evaluated and compared to that of the PID with and without compensator.

PC-based control of robotic and mechatronic systems under MS-Windows NT workstation

A method is proposed to perform control using Intel/sup (R)/ based PCs operated by Windows NT/sup TM/ directly. The software package developed is called WinRec v.1 (Windows real-time control). This low cost method keeps all the advantages of Windows NT without attaching any other kernels and avoids switching different operating systems between experimentation and control design/analysis. A thorough description of the method to set up the multimedia timer provided by Microsoft Development Network Library is presented. Self-customized algorithms based on advanced control techniques can be implemented with the standard protocol that is established here. The proposed protocol is evaluated using two different systems in control experiments. In the first system, an industrial robot manipulator is controlled by applying an independent joint PID control scheme. Results are also shown from experiments where LQR and H/sub 2/ controllers are applied to suppress vibrations of a flexible payload carried by the robot manipulator. In the second system, position, force, temperature, voltage and current data are simultaneously recorded in order to evaluate the performance of a shape-memory-alloy wire bundle actuator in open loop control experiments.