Open-loop Control Method Research Articles

Maintenance of satellite formations using environmental forces

This paper examines the maintenance of satellite formations using two environmental forces: solar radiation pressure and aerodynamic forces. It is assumed that the satellites are equipped with solar flaps or aerodynamic flaps. Control using aerodynamic flaps is considered for satellite formations in LEO while solar flaps is applied to formations in LEO as well as GEO. The simple control laws based on open-loop and closed-loop control methods are designed for required rotation of the flaps to achieve desired formation keeping. The feasibility of the proposed schemes is proven via stability analyses followed by numerical simulations. A linear flap rotation scheme is found to keep the relative position errors bounded to ±5m. The proposed control methods show the effectiveness of the use of solar radiation pressure and aerodynamic forces for satellite formation flying.

Maximum Allowable Load of Mobile Manipulator in the Presence of Obstacle Using Non-Linear Open and Closed Loop Optimal Control

In this paper, a new method which is a combination of open and closed loop optimal control is developed to find maximum load carrying capacity of nonholonomic wheeled mobile manipulator (WMM) in the presence of environmental obstacles. At first level, open loop control method is used to solve path planning problem and design an optimal trajectory with maximum dynamic load carrying capacity between initial and final point. Optimality conditions are obtained for carrying the maximum payload between two points in an environment including obstacles. The main contribution at first level is applying obstacle avoidance in the objective function that leads to a two-point boundary value problem. At second level, a nonlinear closed loop optimal controller is designed to perform optimal trajectory in real-time conditions. The main contribution at second level is applying the nonlinear Hamilton–Jacobi–Bellman equation to design an optimal nonlinear state feedback controller. Numerical procedure in both levels, that is time consuming, is performed off line and resulted control law is simply applied in real-time conditions. The other contribution of this paper is the combination of these levels; it makes sure that the achieved trajectory and maximum load is applicable. To show the effectiveness of the method, simulations are performed for a planar WMM and a spatial WMM named Scout as well as experimental results for Scout robot.

MRI 소음의 특성을 이용한 공동 내부 목표점의 능동소음 제어

Recently, MRI(magnetic resonance imager) scanner is continually used for medical diagnosis and many biomedical researches. When it operates, however, intense noise is generated. The SPL(sound pressure level) of the noise approaches 130 dB especially in 3 T(Tesla) MRI. Meanwhile, more than 3 T MRI scanners have been developed to get higher-resolution images, so louder noise is expected in the future. The intense noise makes patients feel nervous and uncomfortable. Moreover, it could possibly cause hearing loss to patient in extreme cases. For this reason, some active noise control systems have been researched. One of them used feedback Filtered-X LMS(FXLMS) algorithm which is able to control only narrowband noises and possible to diverge in severe case. In this paper, we determine the property of MRI noise. Using the property, we applied a method of open-loop and adaptive control for reducing MRI noise at target point inside bore. We verified performance of the method with computer simulation and preliminary experiment. The results demonstrate that the method can effectively reduce MRI noise at target point.

Two-stage open-loop velocity compensating method applied to multi-mass elastic transmission system

In this paper, a novel vibration-suppression open-loop control method for multi-mass system is proposed, which uses two-stage velocity compensating algorithm and fuzzy I+P controller. This compensating method is based on model-based control theory in order to provide a damping effect on the system mechanical part. The mathematical model of multi-mass system is built and reduced to estimate the velocities of masses. The velocity difference between adjacent masses is calculated dynamically. A 3-mass system is regarded as the composition of two 2-mass systems in order to realize the two-stage compensating algorithm. Instead of using a typical PI controller in the velocity compensating loop, a fuzzy I+P controller is designed and its input variables are decided according to their impact on the system, which is different from the conventional fuzzy PID controller designing rules. Simulations and experimental results show that the proposed velocity compensating method is effective in suppressing vibration on a 3-mass system and it has a better performance when the designed fuzzy I+P controller is utilized in the control system.

Multistage Adaptive Estimation of Sparse Signals

This paper considers sequential adaptive estimation of sparse signals under a constraint on the total sensing effort. The advantage of adaptivity in this context is the ability to focus more resources on regions of space where signal components exist, thereby improving performance. A dynamic programming formulation is derived for the allocation of sensing effort to minimize the expected estimation loss. Based on the method of open-loop feedback control, allocation policies are then developed for a variety of loss functions. The policies are optimal in the two-stage case, generalizing an optimal two-stage policy proposed by Bashan et al., and improve monotonically thereafter with the number of stages. Numerical simulations show gains up to several dB as compared to recently proposed adaptive methods, and dramatic gains compared to non-adaptive estimation. An application to radar imaging is also presented.

Development of a Vector Display System Based on a Surface-Micromachined Micromirror

This paper presents a small-size low-power portable vector display system. The display system uses a micromirror which consists of a simple two-thin-film structure and is fabricated using a surface-micromachining process, i.e., Polysilicon Multi User MEMS Processes. The micromirror exhibits rotational motion around two axes as well as translational motion through four repulsive-force electrostatic actuating units. The micromirror is free of the “pull-in” effect which is associated with conventional micro electrostatic actuators. The micromirror is operated in a nonresonant mode and is capable of static positioning. Measured data show that the micromirror can achieve an optical scanning angle of ±2.5° in each axis. The measured bandwidth (-3 dB) for each driving unit is 2000 Hz operating at a sinusoidal input voltage of 0-200 V. The settling times of the actuating unit are 2.75 and 3.32 ms with overshoots of 5% and 48% for step inputs of 200 to 0 V and 0 to 200 V, respectively. The portable vector display system is developed through integrating the micromirror, a laser source, the optics, and a microcontroller and is shown to be very effective in displaying complex geometries. Open-loop control methods using lookup table searching, spot dwelling, and scan speed control were developed to control the integrated portable device.

Adaptive synchronization and pinning control of colored networks

A colored network model, corresponding to a colored graph in mathematics, is used for describing the complexity of some inter-connected physical systems. A colored network is consisted of colored nodes and edges. Colored nodes may have identical or nonidentical local dynamics. Colored edges between any pair of nodes denote not only the outer coupling topology but also the inner interactions. In this paper, first, synchronization of edge-colored networks is studied from adaptive control and pinning control approaches. Then, synchronization of general colored networks is considered. To achieve synchronization of a colored network to an arbitrarily given orbit, open-loop control, pinning control and adaptive coupling strength methods are proposed and tested, with some synchronization criteria derived. Finally, numerical examples are given to illustrate theoretical results.

Pneumatic Muscle Actuator (PMA) Task-Specific Resistance for Potential Use in Microgravity Exercise

A pneumatic muscle actuator (PMA) is a device that mimics the behavior of skeletal muscle by contracting and generating force when activated. This type of actuator has a high power to weight ratio and unique characteristics which make it ideal for human interaction. PMAs, however, are difficult to control due to nonlinear dynamics. Our objective was to control a PMA as a source of task-specific resistance in simulated isokinetic strength training. Task-specific resistance will benefit those in need of strength training through a joint's range of motion, including astronauts who need to counteract muscle atrophy during prolonged spaceflight. The lightweight, clean, and compact PMA driven by pressurized air is able to produce resistance in microgravity. An open-loop control method based on a three-element phenomenological inverse model was developed to control the PMA. A motor was simultaneously controlled to act as simulated human quadriceps working against the PMA-produced resistance. For ankle weight replacement resistance profiles, the PMA control method produced resistance and PMA displacement tracking errors (RMSE) of 0.36-1.61 Nm and 0.55-1.59 mm, respectively. Motor position (simulated joint angle) tracking errors ranged from 0.47 to 2.82 degrees. Results indicate that the inverse model based control system produces task-specific PMA resistance and displacement. Closed-loop motor control was able to simulate isokinetic movement successfully. More complicated resistance profiles reveal the need for closed-loop control. Future work focuses on advancing both the PMA control strategies and the capabilities of the human simulator so that actual human operator applications can be realized.

A method for open-loop control of dynamic motions of piezo-stack actuators

Precision control of three-dimensional dynamic motions of piezoelectric actuators is crucial for many applications of nanotechnology and precision engineering. In this paper, an open-loop technique to control the three-dimensional single-frequency motions of multi-axis piezo-stack actuators is presented. In this approach, the dynamic behavior of piezo-stack actuators is represented by the harmonic frequency response functions (hFRFs) that are obtained through an laser Doppler vibrometry (LDV)-based experimental characterization method. To obtain the desired motions at a given frequency, the actuator is excited at both the fundamental (motion) frequency and its harmonics, latter of which aiming to compensate for the unwanted higher-harmonic response components that arise due to non-linear dynamic behavior. The fundamental and the first-order compensatory excitation components are determined analytically using the inverse hFRFs. For the higher-order response terms, a compensation approach based on an iterative experimental technique is proposed. The effectiveness of the presented control method is demonstrated through a set of evaluation tests on two different three-axis piezo-stack actuators, where a set of motion-error metrics were defined and quantified. It was shown that the proposed method can be used to generate single-frequency motions with wide range of nanometric sizes with average errors less than 5% of the targeted motion amplitudes.

Temperature compensation in integrated CMOS-MEMS scanning probe microscopes

The authors report on the operation of complementary metal-oxide semiconductor microelectromechanical system (MEMS) scanning probe microscope (SPM) with integrated three-dimensional electrothermal actuation and three-axis position sensing. Conventional SPM makes use of piezoelectric positioning systems which are bulky (leading to thermal drift and poor vibration immunity) and suffer from inherent creep (leading to image distortion). The scanner design is intended to leverage the myriad physical benefits of dimensional scaling to improve the performance and to reduce the barrier to entry for SPM ownership when compared to the state-of-the-art. However, the integration of multiple electrothermal actuators on chip introduces several complications owing to coupling between electrical, thermal and mechanical domains. The focus of this Letter is to discuss the origins of these effects, and the strategies that are implemented to mitigate them. Specifically, the authors discuss the open-loop and closed-loop control methods that are used to drive the lateral and vertical actuators and propose and verify a method to compensate for the parasitic effects observed in the piezoresistive force sensors. To the best of the authors' knowledge, this is the first integrated MEMS-SPM with multiple imaging modes that can image a sample without the need for off-chip scanners or laser-based position sensing.

SIMULATION METHOD FOR WIND TUNNEL BASED VIRTUAL FLIGHT TESTING

The Wind Tunnel Based Virtual Flight Testing (WTBVFT) could replicate the actual free flight and explore the aerodynamics/flight dynamics nonlinear coupling mechanism during the maneuver in the wind tunnel. The basic WTBVFT concept is to mount the test model on a specialized support system which allows for the model freely rotational motion, and the aerodynamic loading and motion parameters are measured simultaneously during the model motion. The simulations of the 3-DOF pitching motion of a typical missile in the vertical plane are performed with the openloop and closed-loop control methods. The objective is to analyze the effect of the main differences between the WTBVFT and the actual free flight, and study the simulation method for the WTBVFT. Preliminary simulation analyses have been conducted with positive results. These results indicate that the WTBVFT that uses closed-loop autopilot control method with the pitch angular rate feedback signal is able to replicate the actual free flight behavior within acceptable differences.

ADAPTIVE OPEN-PLUS-CLOSED-LOOP CONTROL METHOD OF MODIFIED FUNCTION PROJECTIVE SYNCHRONIZATION IN COMPLEX NETWORKS

This paper investigates the modified function projective synchronization (MFPS) in drive-response dynamical networks (DRDNs) with different nodes, which means that systems in nodes are strictly different. An adaptive open-plus-closed-loop (AOPCL) control method is proposed, which is a practically realizable method and can overcome the model mismatched to achieve synchronization. It is well known that each of the close-loop and open-loop control method possesses some advantages and disadvantages. By combining their advantages, the open-plus-closed-loop (OPCL) control method was proposed by Jackson and Grosu. For arbitrary nonlinear dynamic systems, dx/dt = F(x,t), Jackson and Grosu proved that there exists solutions, x(t), in the neighborhood of any arbitrary goal dynamics g(t) that are entrained to g(t), through the use of an additive controlling action, K(g,x,t) = H(dg/dt,g) + C(g,t)(g(t) - x), which is the sum of the open-loop action, H(dg/dt,g), and a suitable linear closed-loop (feedback) action C(g,t). This method is a practically realizable method and robust to limited accuracy of data and effects of noise. The AOPCL control method preserve the merits of OPCL control method and its closed loop control part can be automatically adapted to suitable constants. Considering time-delays are always unavoidably in the practical situations, MFPS in DRDNs with time-varying coupling delayed is further investigated by the proposed method. Corresponding numerical simulations are performed to verify and illustrate the analytical results.

Nonholonomic quantum control

In this paper, we review an open-loop evolution control method, called nonholonomic control, based on the alternate application of only two physical perturbations for timings which play the role of adjustable control parameters. We present the algorithm which allows one to explicitly compute the pulse sequence achieving any arbitrarily prescribed unitary evolution in a nonholonomic system, i.e. a system subject to two physical perturbations which, together with the natural Hamiltonian of the system, span the entire Lie algebra . We moreover expose two extensions of our method to open quantum systems which, respectively, aim at preserving the information stored in the system and safely processing this information. The first is based on a generalization of the quantum Zeno effect, while the second is inspired by decoupling pulse techniques. The most important feature of the methods presented here is their universality: they indeed do not rely on any specific assumption on the system, which in particular is not bound to be a collection of two-level systems, or the error model considered, as is usually the case in the literature. Numerical and physical applications of our techniques are also provided.

Optimization of Concrete Open-Loop Pumping Displacement Control Parameters under Variable Loads

To solve the problem of piston striking cylinder and pumping insufficiency, an optimization method of concrete open-loop pumping displacement control is derived and presented. In order to control piston stroke effectively, the optimization model of concrete open-loop pumping displacement control parameters is built based on considering the system’s open-loop characteristics. Satisfying the physical constraint of preventing piston striking cylinder and maximizing piston’s effective stroke are taking as the evaluation criterion during the modeling process. Using this method, simulation and experimental research has been proceeded in a type of concrete pump. The result shows that concrete pumping piston can not only meet the noninterference physical constraint, but also increase the pumping efficiency significantly under variable loads. The optimization model provides a new method that can be used in engineering practice for solving the design problem of concrete pumping open-loop control system under variable loads.

Distributed actuation characteristics of clamped-free conical shells using diagonalpiezoelectric actuators

In spacecraft, severe vibrations induced by the launch vehicle may cause damage to theprecision payload. Therefore active adapters with vibration suspending characteristics areneeded. This paper presents theoretical studies of the active vibration controlcharacteristics of conical shells with laminated piezoelectric actuators. A diagonalpiezoelectric actuator is proposed to control the axial, lateral and transverse vibrations ofthe conical shell. Modal functions are designed to represent the free vibrations of theconical shell with clamped-free boundary conditions. General formulae of the modal controlforce and corresponding components are derived based on the converse piezoelectriceffects and then specified for the diagonal actuators. By using an open-loop controlmethod, the modal control characteristics of diagonal actuator segments at differentlocations are investigated and compared, and the axial, lateral and transversevibrations of two conical shell models are evaluated. The optimal locations ofactuator segments for the control of different natural modes are also investigated.

Feed-Forward Control of Open Channel Flow Using Differential Flatness

This brief derives a method for open-loop control of open channel flow, based on the Hayami model, a parabolic partial differential equation resulting from a simplification of the Saint-Venant equations. The open-loop control is represented as infinite series using differential flatness, for which convergence is assessed. A comparison is made with a similar problem available in the literature for thermal systems. Numerical simulations show the effectiveness of the approach by applying the open-loop controller to irrigation canals modeled by the full Saint-Venant equations.

Review and Stability Analysis of PLL-Based Interleaving Control of DCM/CCM Boundary Boost PFC Converters

In this paper, a systematic review of phase-locked loop (PLL)-based closed-loop control methods for interleaved discontinuous conduction mode/continuous conduction mode (DCM/CCM) boundary boost power factor correction (PFC) converters is presented. A detailed analysis of the stability of the PLL with instant averaging filter is performed and verified by simulation. The stability of the PLL with instant averaging filter and with RC filter is compared by simulation. Based on the simulation results, it is concluded that the PLL-based closed-loop methods always provide stable operation, unlike the open-loop control methods, where the only method that results in stable operation is the slave synchronization to the turn- on instant of the master with current-mode control. It is also shown that the dynamic response of the PLL-based closed-loop methods with master-slave approach and democratic approach is almost identical. Experimental results obtained on a 300-W, universal input, 400-V output, interleaved DCM/CCM boundary boost PFC prototype circuit with a dedicated controller IC utilizing a democratic, PLL-based closed-loop method are also provided.

High-precision open-loop adaptive optics system based on LC-SLM

Used as a wavefront corrector, a liquid crystal spatial modulator (LC-SLM) has good repeatability and linearity, which are essential for open-loop adaptive optics, and the open-loop optical system can increase the light energy efficiency by a factor of two for the LC-SLM and improve the system bandwidth. In order to test the performance of the LC-SLM in open-loop correction, an indoor closed-loop configuration optical system is constructed on the open-loop control method. With this method, it is demonstrated that the residual error after open-loop correction could be smaller than 0.08lambda (RMS: root mean square value) if the initial wavefront aberration is below 2.5lambda (RMS), and the repeatability error of open-loop correction is smaller than 0.01lambda (RMS).

Optimal Injection Design for Resin Transfer Molding with In Situ Permeability Measurement and Process Simulation

Resin transfer molding (RTM) process has been gaining extensive attention because of its ability to produce complex structural composite parts. Researchers have made significant progress toward obtaining quality products. The preform permeability change during actual molding process brings up difficulty in achieving consistency in part quality. This article presents an adaptive RTM injection design approach in which process simulation and Hardware-In-the-Loop-Simulation (HILS) technique are used: the whole-field preform permeability profile is provided by an in situ gas-assisted permeability measurement system and then inputted to the process simulation right before each control step during molding; an open loop control method steering the resin flow is also proposed. It is found that the HILS can be used to realize optimal injection design and flow control with accurate online permeability estimation.

Control approaches for a cylinder wake by electromagnetic force

The reduction of drag force and suppression of vortex shedding on a circular cylinder in electrically poorly-conducting water can be realized by utilizing the Lorentz forces. In order to control the cylinder wake effectively, three kinds of control approach, i.e. open-loop, closed-loop and optimal control methods, are proposed and discussed in the present paper. Constant Lorentz forces are used in the open-loop control process, and Lorentz forces are varied to target the zero total drag or the zero pressure drag coefficients during the control process in two closed-loop control procedures. The purpose of optimal flow control is to determine controls that effectively tailor the flow, and the key element of an optimal flow control is the minimization of a cost functional that provides a quantitative measure of the objective. Numerical simulation of the theoretical models is performed in the exponential–polar coordinates system, from which it has been shown that the above three methods can suppress the vortex shedding successfully; moreover, during the control process, the optimal control needs less energy than the closed-loop control method targeting a zero total drag or pressure drag coefficients.