Dual-stage Control Research Articles

Dual-stage control method for continuous hopping on the surface of small celestial bodies

Surface movement exploration techniques are an important approach to further the understanding of small celestial bodies. Hopping movement is employed to take advantage of the weak gravitational field of small celestial bodies, facilitating long-distance mobility of the rover. The rover exhibits a strong attitude-orbit coupling characteristic during the hopping movement. Different contact attitudes contribute to the challenge of determining the rebound trajectory, rendering it difficult for the rover to maintain continuous movement towards the target position along the nominal trajectory. In this paper, a dual-stage control method for continuous surface hopping movement is developed, wherein the control is applied separately during the flight stage and the collision stage. During the flight stage, applying attitude control enables the rover to establish contact with the surface in a specific attitude, ensuring accuracy in movement direction and creating favorable conditions for the control process in the collision stage. The flywheel is controlled in the collision stage to correct the state change and energy loss due to the collision, enabling the rover to attain the desired hopping state. Considering the energy consumption of the rover, the minimum hopping velocity sequence and angular velocity sequence are designed based on the hopping angle and heading angle. The intricacies and uncertainties inherent in the surface environment of small celestial bodies pose challenges for the rover during hopping and flying. In response to the issue, a finite-time adaptive sliding-mode control law is devised. The control law facilitates the rapid adjustment of the rover to the target attitude in flight, demonstrating strong robustness. In addition, by integrating the changes in contact point velocity with the impulse contact model, the accuracy of the rover's rebound state updates is enhanced. Finally, a set of simulations is performed, and simulation results indicate that the dual-stage control method can achieve a final landing position error of less than 0.2 m for a continuously hopping. The finite-time adaptive sliding-mode control law can stabilize the rover's attitude within 10 s. Conducting 500 Monte Carlo simulations of the continuously hopping rover in three small celestial body surface simulation environments shows that the position endpoint error is within 0.3 m.

Design and Control of a Flexure-Based Dual Stage Piezoelectric Micropositioner

In the field of advanced manufacturing technology, there is a growing need for high-precision micro/nano positioners. The traditional single stage actuated positioners have encountered performance limitation in achieving longer travel range and higher precision. This motivates us to develop a novel dual stage piezoelectric-actuated micropositioner presented in this paper. The micropositioner incorporates displacement amplification mechanisms to overcome the limited range of piezoelectric actuators. Design considerations such as flexure characteristics and material selection are discussed, and structural analysis is performed using finite element analysis (FEA). For precise positioning, the dual stage control strategy is investigated and compared with the conventional proportional-integral-derivative (PID) single stage control method. In the proposed positioner, a combination of parallelogram and bridge mechanisms is utilized. The bridge mechanism works to amplify the piezoelectric actuator displacement output. The parallelogram mechanism, integrated within the system, helps mitigate resonance modes and contributes to the achievement of linearized motion. The characteristics of the micropositioner were evaluated using analytical modelling and FEA. Multiple analysis was used to optimise the positioner’s design parameters. Furthermore, experimental studies were carried out to validate the characteristics of the micropositioner performance in terms of achievable output travel range and sustained positioning accuracy.

Precision tracking control of a dual-stage measuring machine

Abstract Modern production requires shorter measuring cycles of measuring machines, which can be achieved with highly dynamic references causing dynamic deviations of the actual tool-center-point (TCP) position. To minimize the TCP tracking error, the considered measuring machine is extended with a redundant axis and a modular control concept is proposed. For this dual-stage actuation setting, a higher-level reference allocation module exploits the resulting redundancy and yields suitable position references for the lower-level controlled subsystems. On the higher-level, two dual-stage control concepts are presented, yielding both significantly reduced tracking errors in experiments compared to using only the main axis. Furthermore, to deal with strongly spatially varying friction of the main axis of the considered measuring machine, its lower-level control system is improved.

Dual-Stage Control Strategy for a Flying Capacitor Converter Based on Model Predictive and Linear Controllers

This article proposes a novel dual-stage control strategy for a flying capacitor converter. During transients, the proposed control scheme applies finite-control-set model predictive control to drive the system close to the desired reference, including all the known nonlinearities of the system in the converter model. When the converter state is in a neighborhood of the reference, the dual-stage controller switches to a pulsewidth modulation based linear controller with an integral action. In this case, the linear controller is reformulated in its feedback form. Thus, the internal linear controller states can be updated based on the actual input applied by the predictive controller. This allows the dual-stage controller to achieve a smooth transition when commuting between controllers and a zero-steady-state error even when load parameter errors are present. Experimental results are provided to verify the effectiveness of the proposed dual-stage controller.

Dual stage control of a servo system consisting of a piezoelectric actuator and a linear motor for electrical discharge machining

Gap width is the most important factor that affects the stability of the electrical discharge machining (EDM) process, material removal rate and surface finish of the workpiece. This research is to develop a new hybrid positioning system which consists of a linear servo motor and a piezoelectric actuator (PZT) for high efficiency EDM processes. In this new system, the servo motor provides the macro feeding for the workpiece while the PZT feeds the workpiece in micro scale at high frequency. To reduce the delay caused by separate movements of the linear motor and PZT, a new control algorithm was developed to synchronize the movements of both the motor and PZT. Cutting experiment shows that an increase in MRR of 1.5 times was achieved by using the proposed algorithm.

Comparative Analysis among Single-Stage, Dual-Stage, and Triple-Stage Actuator Systems Applied to a Hard Disk Drive Servo System

In modern times, the design and optimization of different actuator systems for controlling a high-precision position control system represent a popular interdisciplinary research area. Initially, only single-stage actuator systems were used to control most of the motion control applications. Currently, dual-stage actuation systems are widely applied to high-precision position control systems such as hard disk drive (HDD) servo systems. In the dual-stage system, a voice coil motor (VCM) actuator is used as the primary stage and a piezoelectric micro-actuator is applied as the secondary stage. However, a dual-stage control architecture does not show significant performance improvements to achieve the next-generation high-capacity HDD servo system. Research continues on how to fabricate a tertiary actuator for a triple-stage HDD servo system. A thermal positioning controller (TPC) actuator is considered promising as the tertiary stage. The triple-stage system aims to achieve greater bandwidth, track density, and disk speed, with minimum sensitivity and greater error minimization. In this work, these three actuation systems with different combinations of proportional plus integral (PI), proportional plus derivative (PD), and proportional plus integral plus derivative (PID) controller, lag-lead controller, lag filter, and inverse lead plus a PI controller were designed and analyzed through simulation to achieve high-precision positioning. The comparative analyses were done on the MATLAB/Simulink simulation platform.

Robust control with compensation of adaptive model for dual-stage inertially stabilized platform

To achieve excellent tracking accuracy, a coarse-fine dual-stage control system is chosen for inertially stabilized platform. The coarse stage is a conventional inertially stabilized platform, and the fine stage is a secondary servo mechanism to control lens motion in the imaging optical path. Firstly, the dual-stage dynamics is mathematically modeled as a coupling multi-input multi-output (MIMO) control system. Then, by incorporating compensation of adaptive model to deal with parameter variations and nonlinearity, a systematic robust H∞ control scheme is designed, which can achieve good tracking performance, as well as improve system robustness against model uncertainties. Lyapunov stability analysis confirmed the stability of the overall control system. Finally, simulation and experiment results are provided to demonstrate the feasibility and effectiveness of the proposed control design method.

이동형 플랫폼에 탑재된 포탑 시스템의 모션 안정화 제어기 설계

The motion stabilization have been a critical interest in various mechanical fields. It, especially, plays a key role in maintenance of the Line of Sight (LOS) for weapons such as turret’s precise targeting performance. For high mobility, turrets are typically located on various moving platforms, either ground-base or ocean-base. The base motion affects LOS through the mechanical friction via bearing structure. Thus, this paper proposes dual-stage control architecture for two Degrees of Freedom DOF) turret on a ground-base moving platform for robust position tracking performance. Proposed control structure possesses a real-time disturbance observer in order to compensate disturbances including friction caused from the moving base. The structure consists a conventional outer-loop position controller for robust position tracking performance and inner-loop disturbance observe for effective disturbance cancellation. The validity of the algorithm is confirmed via simulation by observing that the resulting position tracking error satisfies the target performance.

Repetitive model predictive control for precise control of complex trajectory tracking in dual-stage actuator systems

This article presents a predictive control methodology for the precise tracking of complex reference commands in dual-stage actuator systems. To improve synchronized motion control performance, a cost function was applied to account for dual-stage actuator tracking error as well as tracking error in the first-stage actuator. The dual-stage actuator control system uses repetitive model predictive control with two repetitive controllers to reduce the occurrence of periodic errors. As in precision machining, a complex reference trajectory containing two dynamic tracking signals with non-trivial magnitude and frequency orders in a motor/piezoelectric-driven dual-stage actuator system was used to evaluate the practicability of the proposed repetitive model predictive control method. Experimental results demonstrate the efficacy of the proposed repetitive model predictive control system in enhancing the periodic tracking control of dual-stage actuator systems, even when subjected to persistent short pulse disturbance.

Coupling effect and control strategies of the maglev dual-stage inertially stabilization system based on frequency-domain analysis

Maglev dual-stage inertially stabilization (MDIS) system is a newly proposed system which combines a conventional two-axis gimbal assembly and a 5-DOF (degree of freedom) magnetic bearing with vernier tilting capacity to perform dual-stage stabilization for the LOS of the suspended optical instrument. Compared with traditional dual-stage system, maglev dual-stage system exhibits different characteristics due to the negative position stiffness of the magnetic forces, which introduces additional coupling in the dual stage control system. In this paper, the coupling effect on the system performance is addressed based on frequency-domain analysis, including disturbance rejection, fine stage saturation and coarse stage structural resonance suppression. The difference between various control strategies is also discussed, including pile-up(PU), stabilize-follow (SF) and stabilize-compensate (SC). A number of principles for the design of a maglev dual stage system are proposed. A general process is also suggested, which leads to a cost-effective design striking a balance between high performance and complexity. At last, a simulation example is presented to illustrate the arguments in the paper.

Time delay and sampling rate effect on dual-stage servo control performance

Dual-stage servo control loops are modeled for hard disk drives (HDDs) with the consideration of time delay which is due to the time taken for position error signal measurement and controller computing. The time delays are involved in controller design and the closed servo control loop is investigated to show the effects of the time delay on servo control performance. The studied actuation system is a PZT milliactuator based dual-stage servo system. The delay time within and over the sampling interval is separately considered for 62.5 kHz sampling rate. To show the effect of sampling rate on servo control performance, a control system designed with 40 kHz sampling rate is also studied. As a result, significant improvement of servo performance is attained with this increased sampling rate and a reasonable time delay for the dual-stage actuation system.

High-order non-singular terminal sliding mode control for dual-stage hard disk drive head positioning systems

A dual-stage actuator system in a hard disk drive will be expected to meet more stringent servo bandwidth requirements for higher recording density in the near future. To simplify the control design, most of the work on the dual-stage actuator track-seeking control is based on the rigid model. However, light-weight materials are used in practice; because of the existence of flexible modes in the system, the challenges involved in designing a reasonable controller need to be addressed. This article proposes a high-order non-singular terminal sliding mode control scheme to suppress undesirable flexural vibrations, while improving the head positioning speed and accuracy. Initially, a model of the system is built and then the flexible dual-stage actuator system is decomposed into input–output and internal sub-systems, to design the high-order non-singular terminal sliding mode controller. Simulation results show that the settling time in track-seeking is reduced and the tracking precision is improved with the proposed method.

Trajectory tracking and vibration suppression of a 3-PRR parallel manipulator with flexible links

To achieve high speed, flexible planar parallel manipulators (PPM) are typically designed with lightweight linkages, but hence suffer from unwanted structural vibration, diminishing positioning accuracy. To achieve high positioning accuracy, this paper addresses the vibration suppression of a PPM with three flexible linkages actuated by linear ultrasonic motors (LUSM). Based on the extended Hamilton’s principle, a rigid–flexible dynamic model of a proposed PPM is developed using the substructure approach and the assumed mode method (AMM). The assumed mode shapes of the flexible linkages are verified through the experimental modal tests. Then, two control algorithms are designed for tracking control of the end effector and vibration attenuation of the flexible linkages. The first approach is a two-timescale control based on singular perturbation principles, implemented as a joint motion control without additional actuators. The second approach is a dual-stage control method. In this control approach, a variable structural control (VSC) method is applied to realize motion tracking of the moving platform, while the strain and strain rate feedback control (SSRF) is developed to suppress the undesired vibration of the flexible linkages, using multiple distributed collocated lead zirconate titanate (PZT) transducers. Stability analysis of the two algorithms is investigated based on Lyapunov approach. Simulation results of these two approaches show that the dual-stage control method provides better vibration attenuation, and hence, faster settling time of the PPM is achieved.

Design of Coarse-Fine Combined Synchronization Control System for Lithography Based on Cross-Coupled Sliding Mode Control

In order to achieve high position precision and synchronization between the wafer stage and the reticle stage, a cross-coupled sliding mode control scheme for a coarse-fine combined synchronization servo system of lithography is proposed. To accomplish high bandwidth and high tracking precision, a conventional linear motor is combined with a voice coil motor as a coarse-fine dual-stage control system. A cross-coupled structure is presented to decrease the synchronization error during scanning operation. Sliding mode control law is designed based on the control error and the synchronization error. Simulation results show that the synchronization error and the control error have the same order of magnitude, and the dynamic performance of the control system satisfies the design requirement.

Robust Adaptive Attitude Tracking Control With L2-Gain Performance and Vibration Reduction of an Orbiting Flexible Spacecraft

This paper presents a dual-stage control system design method for flexible spacecraft attitude tracking control and active vibration suppression by an embedded smart material as sensors/actuators. More specifically, a conventional sliding mode controller with the assumption of knowing system parameters is first designed that ensures asymptotical convergence of attitude tracking error described by error quaternion and its derivative in the presence of bounded parameter variation/disturbance. Then it is redesigned, such that the need for knowing the system parameters in advance is eliminated by using an adaptive updating law. For the synthesis of the controller, to achieve the prescribed L2-gain performance criterion, the control gains are designed by solving a linear matrix inequality problem. Indeed, external torque disturbances/parametric error attenuations with respect to the performance measurement along with the control input penalty are ensured in the L2-gain sense. Even if this controller has the ability to reject the disturbance and deal with actuator constraint, it excites the elastic modes of flexible appendages, which will deteriorate the pointing performance. Then the undesirable vibration is actively suppressed by applying feedback control voltages to the piezoceramic actuator, in which the modal velocity feedback control method is employed for determining the control voltages. Numerical simulations are performed to show that attitude tracking and vibration suppression are accomplished, in spite of the presence of disturbances/parameter uncertainties and even control input constraint.

Optimal Sliding Mode Dual-Stage Actuator Control in Computer Disk Drives

This paper presents a discrete-time design of a dual-stage actuator control system with sliding mode for computer disk drives. A state estimator based discrete-time boundary layer sliding mode control scheme is developed for a dual-stage actuator, which consists of a voice coil motor and a microactuator. Considering dominant microactuator flexible mode dynamics and the interaction between the two actuators, an optimal sliding hyperplane is designed to maximize their cooperation so as to attain desired responses. An application example demonstrates the utility of the proposed sliding mode dual-stage actuator control scheme for track-seek in the microactuator range, settle, and track-follow.

Sliding mode attitude control with L 2-gain performance and vibration reduction of flexible spacecraft with actuator dynamics

This paper presents a dual-stage control system design method for the rotational maneuver control and vibration stabilization of a flexible spacecraft. In this design approach, the sub-systems of attitude control and vibration suppression are designed separately using the low order model. Based on the sliding mode control (SMC) theory, a discontinuous attitude control law in the form of the input voltage of the reaction wheel is derived to control the orientation of the spacecraft, incorporating the L 2-gain performance criterion constraint. The resulting closed-loop system is proven to be uniformly ultimately bounded stability and the effect of the external disturbance on both attitude quaternion and angular velocity can be attenuated to the prescribed level as well. In addition, an adaptive version of the control law is designed for adapting the unknown upper bounds of the lumped disturbance such that the limitation of knowing the bound of the disturbance in advance is released. For actively suppressing the induced vibration, strain rate feedback control method is also investigated by using piezoelectric materials as additional sensors and actuators bonded on the surface of the flexible appendages. Numerical simulations are performed to show that rotational maneuver and vibration suppression are accomplished in spite of the presence of disturbance and uncertainty.

A dual-stage control system for high-speed, ultra-precise linear motion

Modern manufacturing equipment often requires high-speed and ultra-precise linear motion. For implementing such motion, a coarse–fine dual stage is effective because the coarse stage has a low bandwidth with a large workspace, and in contrast, the fine stage has a high bandwidth with a small stroke. This paper presents the implementation of an air-bearing, dual-stage system and its control strategy. A closed-loop feedback in an absolute space is used to realize coarse–fine control. The fine stage is driven by a voice coil motor that tracks the designed trajectory, while the coarse stage is driven by permanent-magnet linear synchronous motor that tracks the trajectory of the fine stage to prevent its motion saturation. Also analyzed are the coupled dynamics of the air-bearing dual stage driven by a direct-drive motor. Identification and robust control design for the fine stage are introduced in detail. Method tests for the single fine stage are performed, and the results demonstrate that ultra-precision control can be realized for the fine stage. Next, experiments are presented with the dual stage using different loads. Experimental results show that our control strategy can achieve high-speed, ultra-precision linear motion through the dual stage with a satisfactory performance.

Robust Backstepping Sliding Mode Attitude Tracking and Vibration Damping of Flexible Spacecraft with Actuator Dynamics

This paper presents a dual-stage control system design method for the attitude tracking control and vibration stabilization of a spacecraft with flexible appendages embedded with piezoceramics as sensor and actuator. In this design approach, attitude control system and vibration suppression were designed separately using a lower order model. Based on the sliding mode control (SMC) and backstepping technique, a new attitude controller in the form of the input voltage of the reaction wheel is derived to control the attitude motion of a spacecraft, in which the reaction wheel dynamics is also considered from the real applications point of view. Here the sliding mode technique is used to achieve an asymptotic convergence of the attitude and angular velocity tracking errors in the presence of parameter variation and disturbance by providing a virtual torque input at the rigid body while the backstepping technique is used to regulate the input voltage of the actuator to provide the required torque. The asymptotic stability is shown using a Lyapunov analysis. Furthermore, an adaptive version of the proposed attitude control law is also designed for adapting the unknown upper bounds of the lumped disturbance so that the limitation of knowing the bound of the disturbance in advance is released. For actively suppressing the induced vibration, strain rate feedback control methods are presented by using piezoelectric materials as additional sensors and actuators bonded on the surface of the flexible appendages. The performances of the hybrid control schemes are assessed in terms of attitude tracking and level of vibration reduction in comparison to the proportional-derivative and conventional SMC. Both analytical and numerical results are presented to show the theoretical and practical merit of this hybrid approach.

Variable structure maneuvering control with time-varying sliding surface and active vibration damping of flexible spacecraft with input saturation

This paper presents a dual-stage control system design method for the three-axis-rotational maneuver and vibration stabilization of a spacecraft with flexible appendages embedded with piezoceramics as sensors/actuators. In this design approach, attitude control system and vibration suppression were designed separately using lower order model. The design of attitude controller was based on variable-structure control (VSC) theory leading to a discontinuous control law. To accomplish asymptotic attitude maneuvering in the closed-loop system and be insensitive to the interaction of elastic modes in the presence of unknown disturbances/uncertainty and input saturation as well, a switching mechanism is employed to design the attitude controller such that outside the sliding region VSC law with a time-varying sliding surface is implemented and inside the region the VSC law with a linear sliding surface is activated. Furthermore, a hyperbolic tangent function in conjunction with a sharpness function permitted to vary with time according to a set of user-defined parameters is implemented to offset the disadvantages of existing saturation-respecting controller and chattering. In addition, for actively damping the excited elastic vibrations during attitude maneuvering, modal velocity feedback and strain rate feedback control design methods are presented and compared by using piezoelectric materials as additional sensors and actuators bonded on the surface of the flexible appendages. Numerical simulations are performed to show that rotational maneuver and vibration suppression are accomplished in spite of the presence of disturbance torque, parameter uncertainty and control saturation nonlinearity.