Position Control Of Actuator Research Articles

Integrated Control and Magnetic Suspension for Fast Attitude Maneuvering and Stabilization

This paper presents a method for spacecraft to achieve the task of fast maneuvering and fast stabilization. To realize this task, a new type of vibration isolation platform whose actuators are based on magnetic suspension techniques and an attitude controller to suit the spacecraft with this new vibration isolation platform are presented. High-frequency vibrations would reduce the stability of the attitude control, and low-frequency vibrations would reduce the maneuvering time of the attitude control. The vibration isolation platform presented in this paper is assembled between the spacecraft bus and the attitude control actuators and acts to reduce the high-frequency vibrations. The vibration isolation platform, which consists of the vibration isolation strut with magnetic suspension, has better performance in the region of high frequency according to the frequency-domain analysis. An appropriate controller for the vibration isolation strut is designed based on the frequency-domain analysis. Then, the attitude controller of the spacecraft bus is designed using the finite-time control theory to reduce the low-frequency vibrations, thus reducing the maneuvering time. Finally, the numerical simulations show that the vibration isolation platform and the attitude controller do work and cooperate well.

Nonlinear Controller Design for Tracking Task of a Control Moment Gyroscope Actuator

Control moment gyroscopes (CMG) are widely used as actuators for attitude control of satellites and spacecraft, which requires the controller to fulfill the tracking task of a CMG in a wide operating range, despite its highly coupled nonlinear behavior. A variety of control techniques were proposed for tracking task of the CMG unit, model 750, from Educational Control Products (ECP), but a few accomplished it in a wide operating range, e.g., the linear parameter-varying approach. Another one that may accomplish it is the nonlinear control approach. Therefore, this article proposes a nonlinear controller design based on feedback linearization for the tracking task of the CMG unit in a wide operating range. To cope with a singularity that would appear in the control signal computation, the proposed controller has a cascade structure composed of an outer tracking controller and an inner velocity controller, both based on the input-output linearization approach. The designed controller is validated via numerical simulations and real-time practical experiments.

Sensorless adaptive sliding mode position control for piezoelectric actuators with charge leakage

Position control of piezoelectric actuators is greatly affected by nonlinearities such as hysteresis and creep. Therefore, precise position sensors must be utilized which have high cost and complicated structures in micro scales. Charge-based position estimation is an alternative method which resorts to piezoelectric linear charge-position property to estimate the actuator position, but in low-impedance actuators, there is a charge leakage caused by actuator internal resistance which deteriorates the position estimation and closed-loop control performance. In this article, the leakage is considered as a sensor fault. Therefore, a combination of charge measurement method and an appropriate observer is designed to detect and isolate the mentioned fault and estimate the actuator position properly. In addition, an adaptive sliding mode control procedure is proposed for trajectory tracking in the presence of estimated states. The required analysis is carried out to guarantee the closed-loop stability. Finally, experimental results show the effectiveness of the proposed method.

Optimized Design and Thermal Analysis of Printed Magnetorquer for Attitude Control of Reconfigurable Nanosatellites

An attitude control system (ACS) is one of the critical subsystems of any spacecraft and typically is in charge of de-tumbling, controlling, and orienting the satellite after initial deployment and during the satellite operations. The magnetorquer is a core magnetic attitude control actuator and, therefore, a good choice for nanosatellite attitude stabilization. There are various methods to achieve control torque using the magnetorquer. An innovative design of a printed magnetorquer has been proposed for the nanosatellites, which is modular, scalable, cost effective, less prone to failure, with reduce harness and power consumption since the traces are printed either on the top layer or inner layers of the printed circuit board. The analysis in terms of generated torque with a range of input applied voltages, trace widths, outer and inner-most trace lengths is presented to achieve the optimized design. The optimum operating voltage is selected to generate the desired torque while optimizing the torque to the power ratio. The results of the analysis in terms of the selection of optimized parameters, including torque to power ratio, generated magnetic dipole moment, and power consumption, have been validated practically on a CubeSat panel. The printed magnetorquer configuration is modular which is useful to achieve mission level stabilization requirements. For spin-stabilized satellites, the rotation time analysis has been performed using the printed magnetorquer.

Development of a cascade position control system for an SMA-actuated rotary actuator with improved experimental tracking results

Hysteresis and significant nonlinearities in the stress–strain–temperature characteristics of shape memory alloy (SMA) actuators prevent effective utilization of these actuators and make them difficult to control. Due to these effects, the position control of SMA actuators has been a great challenge for many industrial applications. In this study, a cascade control for position tracking using torque and position measurement of an SMA-actuated rotary actuator is considered. The effects of the SMA characteristic model on control performance are also focused when simulation consequences are directly applied in practice. Based on nonlinear and unknown dynamics of an SMA actuator, a torque regulation adaptive controller using modified Brinson model is developed that requires to approximate the parameters of the system by only measuring SMA force and actuator rotation. Although it is shown that only an approximate model of the system is sufficient to develop the proposed controller, the system dynamic is simulated using MATLAB software, and the characteristics of SMA wire is considered by both modified Brinson constitutive model and Liang and Rogers constitutive model. The controller gains are regulated for both of the mentioned models using simulation. Finally, the performance of both controllers is further evaluated experimentally, and the accuracy of the proposed controller based on the modified Brinson model is compared to the controller based on the Liang and Rogers model. It is shown that since the Brinson model has a better prediction of the SMA wire behavior, the simulation results based on the modified Brinson model have better conformity to reality.

Cascade Control of Antagonistic VSA-An Engineering Control Approach to a Bioinspired Robot Actuator.

A cascade control structure for the simultaneous position and stiffness control of antagonistic tendon-driven variable stiffness actuators (VSAs) implemented in a laboratory setup is presented in the paper. Cascade control has the ability to accelerate, additionally stabilize, and reduce oscillations, which are all extremely important in systems such as a tendon-driven compliant actuators with elastic transmission. Inner-loop controllers are closed in terms of motor positions, and outer-loop controllers in terms of actuator position and estimated stiffness. The dominant dynamics of the system (position and stiffness), composed of the mechanical part and inner loops, are identified by a closed-loop auto-regressive with exogenous input (ARX) model. The outer-loop controllers are tuned on the basis of experimentally identified transfer functions of the system in several nominal operating points for different stiffness values. After the system is identified, a controller bank is generated in which a pair of actuator position and stiffness controllers correspond to a nominal operating point and covers the area surrounding the nominal point for which it is designed. The controllers used are integral-proportional differential (I-PD) and integral-proportional (I-P) controllers, which are a variation of the PID and PI controllers with dislocated proportional and derivative gains from a direct to feedback branch that result to no overshoot for even fast reference changes (i.e., step signal), which is essential for preventing tendon slackening (meeting the pulling constraint). Analytical formulas for controller tuning based on only one parameter, λ, are also presented. Since position and stiffness loops are decoupled, it is possible to change λ for both loops independently and adjust their performance separately according to the needs. Also, the controller structure secures the smooth response without overshooting step reference or step disturbance signal, which make practical implementation possible. After all the controllers were designed, the cascade control structure for simultaneous position and stiffness control was successfully evaluated in a laboratory setup. Thus, the presented control approach is simple to implement, but with a performance that ensures a pulling constraint for tendon-driven actuators as a foundation for bioinspired antagonistic VSAs.

Improved position control of shape memory alloy actuator using the self-sensing model

A shape memory alloy (SMA) actuator is driven by applying electrical current (or heat) to the actuator, and its electrical resistance is altered by its deformation (or strain). The position of the SMA actuator can be controlled by referring to its electrical resistance, without extra sensors, if the resistance is used as the “feedback signal” in the control system. It is called “self-sensing capability.” However, the relationship between electrical resistance and strain of the SMA actuator inevitably exhibits a hysteresis gap, increasing the control errors. Therefore, we proposed a new self-sensing-based position control model for the SMA actuator to reduce the negative effect of the hysteresis gap and improve the accuracy of position control. The relationship between electrical resistance and strain of the SMA actuator during the application and removal of heat was first constructed. Then, we proposed a control algorithm adopting the self-sensing model considering the relationships during the heating and cooling stages. We estimated that the total mean absolute errors (MAEs) of the position control for multi-step and sinusoidal wave inputs were 3.798% and 6.380%, respectively. They were correspondingly improved by 0.649%p and 2.478%p compared to the MAEs estimated from the conventional self-sensing control algorithm. The proposed self-sensing-based position control algorithm contributes to the improvement in accuracy of the position control when the SMA actuator can be self-controlled.

Position Control of Pneumatic Actuators Using Three-Mode Discrete-Valued Model Predictive Control

A novel discrete-valued model-predictive control (DVMPC) algorithm termed DVMPC2 for the position control of pneumatic actuators using inexpensive on/off valves is presented. DVMPC2 includes a more flexible cost function, an improved prediction strategy, and other improvements. The actuator is a double-acting cylinder with two on/off solenoid poppet valves connected to each chamber. To reduce the switching frequency and prolong the valve life, DVMPC2 directly switches the valves when necessary, instead of using relatively high-frequency pulse-width modulation. Experimental comparisons are made with the state-of-the-art sliding-mode control (SMC) algorithm and the previous DVMPC algorithm. The comparisons are based on the five performance metrics: integral of time-weighted absolute error (ITAE), root mean square error (RMSE), overshoot (OS), steady-state error (SSE), and valve switches per second (SPS). The robustness is evaluated by increasing and decreasing the total mass of the moving components while keeping the controller parameters constant. The experimental results show that the proposed algorithm is superior to the previous DVMPC and outperformed SMC by a wide margin. Specifically, DVMPC2 reduced ITAE by 80%, RMSE by 52%, OS by 43%, and SPS by 20% relative to SMC. There was no clear winner in terms of SSE.

High precision attitude dynamic tracking control of a moving space target

On-orbit spacecraft face many threats, such as collisions with debris or other spacecraft. Therefore, perception of the surrounding space environment is vitally important for on-orbit spacecraft. Spacecraft require a dynamic attitude tracking ability with high precision for such missions. This paper aims to address the above problem using an improved backstepping controller. The tracking mission is divided into two phases: coarse alignment and fine alignment. In the first phase, a traditional saturation controller is utilized to limit the maximum attitude angular velocity according to the actuator’s ability. For the second phase, the proposed backstepping controller with different virtual control inputs is applied to track the moving target. To fulfill the high precision attitude tracking requirements, a hybrid attitude control actuator consisting of a Control Moment Gyro (CMG) and Reaction Wheel (RW) is constructed, which can simultaneously avoid the CMG singularity and RW saturation through the use of an angular momentum optimal management strategy, such as null motion. Finally, five simulation scenarios were carried out to demonstrate the effectiveness of the proposed control strategy and hybrid actuator.

Position control of a series elastic actuator based on global sliding mode controller design

A series elastic actuator &#x0028 SEA &#x0029 is a powerful device in the area of human-machine integration, but it still suffers from difficult position control issues. Therefore, in this paper, an efficient approach is proposed to solve this problem. The approach design is divided into two steps: feedback linearization &#x0028 FL &#x0029 and global sliding mode &#x0028 GSM &#x0029 controller design. The bounded analysis is presented and global asymptotic convergence is analytically proven. Simulation and experiment results illustrate the effectiveness of the proposed scheme.

Fractional-Order Control of Hydraulically Powered Actuators: Controller Design and Experimental Validation

This paper presents a model-free design procedure for the position control of hydraulic actuators. A fractional-order PID (FOPID) controller is designed by employing the Oustaloup recursive method. The controller parameters are tuned experimentally based on the iterative feedback tuning (IFT) technique. The IFT optimizes an objective function using the experimental data taken from an instrumented valve-controlled hydraulic actuator test rig. The objective function, to be minimized, includes both tracking and robust stability criteria. The efficacy of the proposed controller is examined by comparing the experimental results with those from a quantitative feedback theory (QFT) based controller. Although the QFT controller gives rise to good tracking responses, the comparisons show that the FOPID controller results in better settling time in tracking the desired response than the QFT controller. Moreover, it is much less sensitive to the effect of the hunting phenomenon, originating from the dry friction, than the QFT controller. The robustness of the FOPID controller against system uncertainties including the external load, the inertia, and friction is also demonstrated.

A Distributive Approach for Position Control of Clamps in a Reconfigurable Assembly Fixture

Hydraulic actuator is a type of clamp used in a reconfigurable assembly fixture for exact positioning and effective immobilisation of workpiece during the assembly process. However, due to their nonlinearity, there is a need to design a control system for their effective performance. This study presents a distributive approach to mathematical modelling and position control of multiple hydraulic actuators used as a clamping system in a reconfigurable assembly fixture. The electrohydraulic system is verified experimentally in order to observe the synchronisation of the hydraulic actuators. The mathematical model of the system is developed in the Simulink environment. A Simulink model of the system is developed from the mathematical model and simulated with a fuzzy-PID controller in order to obtain the response of all the actuators and other operating characteristics of the system. Simulation results are shown graphically in order to verify the theoretical development.

Cooperative Game Theory-Based Optimal Angular Momentum Management of Hybrid Attitude Control Actuator

The next-generation space missions, such as the space moving target tracking mission and the agile attitude maneuvering mission and so on, propose a high requirement on spacecraft attitude control system. For such missions, hybrid attitude control actuators consisting of control moment gyro and reaction wheel, which can not only offer large control torque but also achieve high control precision, is the best alternative choice. For this hybrid actuator system, the angular momentum management is vital. To handle the momentum management problem, an optimal angular momentum strategy based on cooperative game theory is proposed. The cooperative game model is constructed according to the quadratic programming problem to achieve the minimization of control moment gyro gimbal angular speed and reaction wheel angular acceleration. The proposed cooperative game theory steering logic has overcome the control moment gyro singular problem and reaction wheel saturation problem of the hybrid system. In addition, the energy cost of the hybrid actuator system is reduced. Five groups of simulation scenarios are carried out to demonstrate the effectiveness of the proposed steering logic.

Design and Implementation of 3U CubeSat Platform Architecture

This paper describes the main concept and development of a standard platform architecture of 3U Cube Satellite, whose design and performance were implemented and verified through the development of KAUSAT-5 3U CubeSat. The 3U standard platform is built in 1.5U size and developed as a modular concept to add and expand payloads and attitude control actuators to meet the user’s needs. In the case of the electrical power system, the solar panel, the battery, and the deployment mechanism are designed to be configured by the user. Mechanical system design maximizes the electrical capability to accommodate various payloads and to integrate and miniaturize EEE (Electrical, Electronic, and Electromechanical) parts and subsystem functions/performance into limited-size PCBs. The performance of KAUSAT-5 adopting standard platform was verified by mounting the VSCMG (Variable Speed Control Moment Gyro), which is one payload for technical demonstration, at the bottom of the platform and the infrared (IR) camera, which is the other payload for science mission, on the top. The 3U CubeSat equipped with the electronic optical camera is under development implementing the standard platform to reduce development cost and schedule by minimizing additional verification.

Position control and performance analysis of hydraulic system using two pump-controlling strategies

The role of hydraulic systems is quite evident especially in the case of heavy machineries employed in industries, where the utilisation of high forces amid large stiffness is the prerequisite. Nevertheless, there has been substantial effort put forward in the development of advanced control strategies which finally addressed the issue of the position control. Proportional–integral–derivative control strategy happens to be one among them, which is a versatile and widely renowned approach involved in the position control in this study. Although, it is quite frequently observed that the hydraulic actuation system possesses strong nonlinearities. In this article, two different actuator position control strategies, that is, swash plate control of main pump and speed control strategy of prime mover are compared. In swash plate control strategy, the proportional–integral–derivative controller adjusts the swash plate of main pump through servo mechanism, whereas in the speed control strategy, the proportional–integral–derivative controller adjusts the speed of the electric motor through variable-frequency drive. For this purpose, two MATLAB-Simulink models are developed and validated experimentally. It is found that swash plate control strategy has better dynamic and control performance than the speed control strategy catering same position demand of the linear actuator.

A parallel distributed compensation approach to fuzzy control of spacecraft combined attitude and sun tracking

A spacecraft combined attitude and sun tracking system (CASTS) is a synergized system in which solar array drive assemblies are used as sun trackers and simultaneously as attitude control actuators. This paper, a continuous research on CASTS, addresses its attitude control problem. The kinematics and dynamics equations of a rigid spacecraft attitude motion is inherently nonlinear. In the attitude regulation problem, the attitude motion can be treated as a simple linear system for a constrained range of operating conditions, but it has impacts on the accuracy of the linear model when a model-based controller is implemented. Naturally, this is a compromise between simplicity and accuracy that all design engineers have to face. In this paper, we present a systematic approach to improve the accuracy while preserving the model as linear as possible, by deriving a quasi-linear approximation of a nonlinear spacecraft attitude motion. The quasi-linear approximation is based on the framework of the Takagi–Sugeno (T–S) fuzzy model. If a spacecraft can be modeled in the form of a rule-based T-S fuzzy system that acts as an interpolator between linear state-space systems, an approach called parallel distributed control (PDC) can be used to stabilize the attitude motion. The design philosophy of PDC is to create a simple fuzzy controller, where each rule’s consequent is a control law designed to stabilize the linear system in the corresponding consequent of the spacecraft T-S fuzzy system. Numerical results validate that the attitude and sun-tracking performances are achievable using the proposed PDC strategy.Â

Position and Speed Control of Infusion Pump Actuator for Biomedical Applications

Position and Speed Control of Infusion Pump Actuator for Biomedical Applications

An anti-saturation steering law for Three Dimensional Magnetically Suspended Wheel cluster with angle constraint

Three Dimensional Magnetically Suspended Wheel (3-DMSW) is a new kind of inertia actuator for spacecraft attitude control, which can provide a 3 degrees of freedom torque. On account of the constraint characteristics of 3-DMSW such as a small deflection saturation angle of rotor shaft and the saturation of rotor's variable rotational speed, an anti-saturation steering law based on weighted pseudo inverse is proposed for 3-DMSW cluster. A new weight adjustment method is proposed to adjust the weights of shaft deflections dynamically. A specially designed exponential function with current deflection angle and angular velocity information on the exponent position is adopted as the evaluation criterion of current torque output ability of shaft deflection. Thus the torque command can be distributed dynamically with no angle saturation. The weight adjustment method is demonstrated theoretically and the effectiveness of the anti-saturation steering law is validated by conducting several numerical simulations of attitude agile maneuver. Comparing with the 3-DMSW cluster and flywheel cluster using the traditional steering law, the results show that the 3-DMSW cluster using the proposed method makes the process of agile maneuver more rapid and accurate and the saturation angles of 3-DMSW cluster will not be reached.

Fuzzy Logic Position Control of Pneumatic Actuators

This paper introduces a fuzzy logic based controller for the position control of pneumatic actuators. The proposed control technique is simple, robust, and suitable for nonlinear systems. A mathematical model is obtained in order to simulate the behavior of a pneumatic actuator by taking into account the nonlinearities of the system. Fuzzy logic control is applied with two feedback signals that are the error between the desired and actual position, and the pressure difference in both chambers of the cylinder. The performance of the proposed controller is compared with the classical PID controller by varying several conditions in order to prove the accuracy and robustness of the fuzzy logic controller.

A deorbiter CubeSat for active orbital debris removal

This paper introduces a mission concept for active removal of orbital debris based on the utilization of the CubeSat form factor. The CubeSat is deployed from a carrier spacecraft, known as a mothership, and is equipped with orbital and attitude control actuators to attach to the target debris, stabilize its attitude, and subsequently move the debris to a lower orbit where atmospheric drag is high enough for the bodies to burn up. The mass and orbit altitude of debris objects that are within the realms of the CubeSat’s propulsion capabilities are identified. The attitude control schemes for the detumbling and deorbiting phases of the mission are specified. The objective of the deorbiting maneuver is to decrease the semi-major axis of the debris orbit, at the fastest rate, from its initial value to a final value of about 6471 km (i.e., 100 km above Earth considering a circular orbit) via a continuous low-thrust orbital transfer. Two case studies are investigated to verify the performance of the deorbiter CubeSat during the detumbling and deorbiting phases of the mission. The baseline target debris used in the study are the decommissioned KOMPSAT-1 satellite and the Pegasus rocket body. The results show that the deorbiting times for the target debris are reduced significantly, from several decades to one or two years.