Gimbal Servo Research Articles

Self-Calibration Method for RDC System of Gimbal Servo System in SGCMG Based on Signal Reconstruction

Self-Calibration Method for RDC System of Gimbal Servo System in SGCMG Based on Signal Reconstruction

Expectation-Maximization Based Disturbance Identification and Velocity Tracking for Gimbal Servo Systems With Dynamic Imbalance

Expectation-Maximization Based Disturbance Identification and Velocity Tracking for Gimbal Servo Systems With Dynamic Imbalance

Disturbance Suppression of Gimbal Servo Motor Based on Improved ADRC and ISMC Method

Disturbance Suppression of Gimbal Servo Motor Based on Improved ADRC and ISMC Method

Adaptive Refined Disturbance Observer-Based Velocity-Tracking Control for Gimbal Servo System With Multiple Disturbances

Adaptive Refined Disturbance Observer-Based Velocity-Tracking Control for Gimbal Servo System With Multiple Disturbances

Analysis, Estimation, and Rejection of Multi-Frequency Unknown Disturbances in CMG Gimbal Servo Systems

Analysis, Estimation, and Rejection of Multi-Frequency Unknown Disturbances in CMG Gimbal Servo Systems

A refined anti‐disturbance control method for gimbal servo systems subject to multiple disturbances under constraints

AbstractThe performance of the gimbal servo system in control moment gyro (CMG), which includes precision, lifespan etc., is one of the crucial factors of spacecraft attitude control. The various practical disturbances, however, will not only deteriorate the velocity‐tracking accuracy but will also cause the abnormal gimbal velocity problem (especially peak phenomenon). To this end, this paper proposes a refined anti‐disturbance control method to deal with velocity output constraints and multiple disturbances. Starting with fully understanding the prior information of multiple disturbances, a refined disturbance observer with a low conservativeness is designed to accurately estimate disturbances. The disturbance‐estimation error is analyzed in detail to ensure convergence to a bounded region. Subsequently, a novel barrier Lyapunov function‐based backstepping controller is proposed that considers the residuals of disturbance estimation to simultaneously achieve multiple disturbances attenuation and compensation, and handle velocity output constraints. Notably, the gimbal's maximum velocity is precisely limited to a pre‐specified low range, which benefits the CMG's lifespan and performance. Finally, both simulation and experimental results show that the proposed method performs better in disturbance estimation, velocity tracking, and robustness.

Torque Ripple Minimization of Low-Speed Gimbal Servo System Using Parameter-Optimized ESO

Torque ripple of permanent magnet synchronous motor (PMSM) and load disturbances are the main influencing factors which restrict the application of PMSM in low speed tracking system. In order to improve the speed tracking precision of gimbal servo system in control moment gyro (CMG) with multi-source disturbances, this paper proposes a composite control method based on parameter-optimized extended state observers (ESOs) with sliding mode control in the speed loop and PI control with a feed-forward compensation in the current loop. Three ESOs are employed to estimate the disturbances on d-axis current, q-axis current and the load torque, so that the controller can have the corresponding parts to compensate for the disturbances. In particular, aiming at the contradiction between the estimation quality of the observer and the sensitivity to the measurement noise, an appropriate cost function is designed to take a compromise between the lumped disturbances and measurement noise and optimize the parameters of the ESOs. Finally, simulation and experimental results on the gimbal servo system of magnetically suspended control moment gyroscope (MSCMG) show the effectiveness of the proposed methods.

The coupling analysis for the gimbal servo system of a control moment gyroscope considering the influence of a flexible vibration isolator

To reduce the influence of vibrations generated by the control moment gyroscopes (CMGs), the researchers have put a lot of effort into isolating the vibration between the CMG and the satellite in order to lessen the impact of vibrations produced by the CMGs. The flexibility of the isolator causes the extra degrees of motion for the CMG, which is coupled with the CMG’s dynamic behavior and the control performance of the gimbal servo system is therefore changed. However, how the flexible isolator influences the performance of the gimbal controller is uncertain. In this research, the coupling effect on the gimbal closed-loop system is analyzed. Firstly, the dynamic equation of the flexible isolator supported CMG system is established, and a classic controller is used to keep the gimbal speed stable. Secondly, the energy method (the Lagrange equation) is adopted to calculate the deformation of the flexible isolator and the rotation of the gimbal. Based on the dynamic model, the simulation is conducted in the Matlab/Simulink, the frequency and the step response of the gimbal system is employed to better explore the inherent characteristics of the system. Finally, we conduct the experiments on a CMG prototype. The experimental results show that the isolator reduces the response speed of the system. Moreover, the closed-loop system could be unstable due to the coupling relationship between the flywheel and the closed-loop gimbal system. The obtained results would be helpful for the design of the isolator and the optimization of the control system of a CMG.

A Disturbance Estimation Approach to Self-Calibration of Gimbal Resolver- to-Digital Conversion System

High-precision position measurement of the gimbal servo system is indispensable to accurate torque output of the control moment gyroscope (CMG). This article addresses the systematic error of the resolver caused by the nonideal output signals of the resolver in the gimbal resolver-to-digital (R/D) conversion system. Due to the limitation of the structure and installation space of the CMG, it is impractical to install additional high-precision sensors to calibrate the raw angular position. Thus, this article proposes a new self-calibration method based on the discrete extended state observer (DESO) to compensate the systematic error of the resolver. The systematic error of the resolver is observed through iterating the resolver systematic estimation error and the compensation table is generated by the output of the DESO. Then, the steady-state error and dynamic performance of the DESO is analyzed and simulated. Finally, the proposed self-calibration method is verified by experiments, which show that the angular position control accuracy is significantly improved, which enhances the speed precision of the gimbal servo system.

Adaptive periodic-disturbance observer based composite control for SGCMG gimbal servo system with rotor vibration

This paper presents an adaptive periodic-disturbance observer (APDO)-based composite control scheme to attain accurate velocity-tracking control for the single gimbal control moment gyro (SGCMG). Firstly, a modified periodic-disturbance observer (PDO) is proposed to estimate both the fundamental wave and harmonics of the rotor vibration. Secondly, to ensure the estimation accuracy under variable rotor speed, an APDO is proposed by combining an adaptive frequency estimator with the modified PDO. Integrating with the PI controller, the proposed APDO-based composite control scheme can effectively reduce the influence of rotor vibration, friction, and parameter uncertainties, thereby improving control accuracy. Furthermore, performance and stability analyses show that the observer can achieve accurate estimation under arbitrary initial conditions. Finally, numerical and hardware-in-the-loop simulation results are given to demonstrate the robustness and effectiveness of the proposed scheme.

Periodic Signal Suppression in Position Domain Based on Repetitive Control

In this paper, a periodic signal suppression method in position domain based on repetitive control (RC) is proposed to realize high-precision speed control for the gimbal servo system of the single gimbal control moment gyro (SGCMG). To reduce the volume and weight while outputting large torque, the gimbal servo system usually needs to install the harmonic drive. However, the nonlinear transmission characteristics of the harmonic drive are also introduced into the gimbal servo system and make the speed fluctuate. Considering the speed fluctuation signal shown as a fixed frequency in the position domain, a position domain RC method combined with acceleration feedback is designed to realize the speed fluctuation minimization. The position domain RC improves the dynamic characteristics, while the acceleration feedback increases the damping of the system. To analyze the stability, the position domain RC is converted into the time domain through the domain transformation method, and a phase compensator is designed to improve the stability and increase the bandwidth of the position domain RC by compensating for the phase lag of the middle and low frequency, respectively. The feasibility and effectiveness of the proposed method are verified by the simulation and experimental results. These results illustrate that after applying the proposed approach, the output speed fluctuation and harmonic components decrease more than 20% and 24.1%, respectively.

Velocity-Tracking Control Based on Refined Disturbance Observer for Gimbal Servo System With Multiple Disturbances

Multiple disturbances are the main constraints that hinder the high-performance velocity tracking of the gimbal servo system in control moment gyro. This article presents a non-cascade structured velocity-tracking controller based on a refined disturbance observer for handling multiple disturbances and improve the tracking performance. Specifically, a disturbance observer is designed to estimate the imbalance disturbance, which can be represented by an exogenous system. The disturbances that cannot be modeled <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a priori</i> are treated as a lumped term and estimated via extended state observer. By resorting to disturbance estimation, a novel sliding mode controller based on the disturbance estimation values is developed to handle the mismatched problem and chattering issue. Finally, experimental tests are conducted to verify the effectiveness of the proposed anti-disturbance control scheme.

High-Precision Composite Control Based on Dual-Sampling-Rate Extended State Observer for Ultra-Low Speed Gimbal Servo System

This article aims to deal with the speed control performance of the gimbal servo system at ultra-low speed to guarantee the accuracy of the output torque of the control moment gyroscope (CMG). The main factors leading to the speed fluctuation of the gimbal servo system are the speed measurement error and disturbance torque. This article proposes a composite controller that consists of the dual-sampling-rate reduced-order extended state observer (DSRESO) and sliding-mode controller (SMC) in the speed loop so as to improve the speed control performance at ultra-low speed. DSRESO is designed to deal with the speed measurement as well as the disturbance estimation in ultra-low speed conditions. Then, the SMC-based DSRESO is applied for speed closed-loop control so as to suppress the speed fluctuation of the gimbal servo system under ultra-low speed and disturbance torque conditions. The feasibility and effectiveness of the proposed control scheme have been verified by the simulations and experiments compared with other methods. Also, the resultant effect is that the speed tracking precision of the gimbal servo system at ultra-low speed is improved significantly.

System identification and mechanical resonance frequency suppression for servo control used in single gimbal control moment gyroscope.

Effective identification of the control model is one of the key aspects in improving the performance of the single gimbal control moment gyroscope (SGCMG) servo system. The accuracy and stability of the servo system can be improved by studying system identification and mechanical resonance frequency. In this study, firstly, the SGCMG gimbal servo system was simplified to a two-mass block model. The theoretical mathematical model of the system's transfer function and mechanical resonance frequency was derived. Secondly, this paper studied the effective suppression method for mechanical resonance. Thirdly, the mathematical model of the orthogonal correlation analysis method was deduced for system identification. Then, an experimental platform was investigated to obtain the frequency characteristic curve and the transfer function. Finally, the frequency characteristic curve obtained using the transfer function model was plotted and compared with the frequency characteristic curve obtained experimentally. Our results indicate that the orthogonal correlation analysis has a high identification accuracy.

High-Precision Speed Control for Low-Speed Gimbal Systems Using Discrete Sliding Mode Observer and Controller

The high-precision control of angular speed in low-speed gimbal servo systems is an essential topic in the operation of the single gimbal control moment gyro (SGCMG). This article proposes a discrete control algorithm to suppress the influence of various disturbances on the low-speed gimbal servo system and the constraint between controller parameters and sampling time is established to ensure the stability of the system. To begin with, the disturbance analysis of the low-speed gimbal servo system is presented, including the torque ripple in the permanent magnet synchronous motor (PMSM), nonlinear friction, coupling torque caused by the spacecraft motion, and the parameter uncertainties. Then, a composite control method combining the sliding mode controller (SMC) with sliding mode observer (SMO) is applied to the speed loop and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$q$ </tex-math></inline-formula> -axis current loop. The interferences are estimated by two SMOs, while SMCs are designed to eliminate the influence brought by the residual disturbances. The stability of the overall system is proven based on the Lyapunov criterion. Finally, simulation and experimental results verify the effectiveness of the proposed composite control method.

Position Extraction of Ultralow-Speed Gimbal Servo System With Linear Hall Sensors

This article explores a novel composite signal extraction method to extract high-precision angular position from the signals detected by Hall sensors in the gimbal servo system of single-gimbal magnetically suspended control moment gyro (SGMSCMG). Due to magnetic field distortion and other factors, the detected signals involve lots of harmonics and unequal amplitude, which decrease the position resolution accuracy significantly. In the proposed method, normalization is first performed to obtain signals with equal amplitude. Then, on the basis of offline analysis, the signal reconstructed model is established to suppress the most harmonics. Finally, the errors of the models and unmodeled noise are restrained by applying the discrete extended state observer (ESO). Simulated results show that the influence of harmonics and unequal amplitude on the angular position can be almost attenuated by the proposed method. Besides, plentiful experiments on an SGMSCMG demonstrate the validity of the proposed method, and the desired angular position of the ultralow speed servo system can be extracted effectively.

Position Estimation for Ultra-Low Speed Gimbal Servo System of SGMSCMG Based on Linear Hall Sensors

In the low speed servo system of single gimbal magnetically suspended control moment gyro (SGMSCMG), the accuracy of rotor position is an important factor which influences the speed accuracy. Linear hall sensors with small volume and high precision are usually adopted to the compact equipment and suitable for SGMSCMG. However, the signals detected by hall sensors contain lots of harmonics and noise which influence the accuracy significantly. For this reason, a novel precise position detection method based on 2-step cascaded Kalman filter with phase compensation scheme is proposed to extract the precise position information from `dirty' signals. The proposed method is advantageous since it is very simple and practical, and the phase compensation scheme can primely compensate the phase delay caused by cascaded Kalman filter. Finally, the experiments are carried out in a 50 Nm SGMSCMG, and the results show that the method can effectively estimate the angular position of the ultra-low speed servo motor, and the position accuracy can be improved by 85.7%.

Coupled Dynamic Modeling and Analysis of the Single Gimbal Control Moment Gyroscope Driven by Ultrasonic Motor

A control moment gyroscope (CMG) is a key actuator for spacecraft's attitude and stability control. But there exist micro-vibrations from high-speed flywheel, which will affect the performance of the spacecraft greatly. Due to the unbalanced mass and the supporting structure, the high-speed rotating flywheel could generate disturbance torque, which will be passed to the gimbal to deteriorate the gimbal servo system. At the same time, the rotation of the gimbal will increase the disturbance torque for gyroscopic effect. According · to the bearing theory, the stiffness of the bearing is affected by the load that applied on it, which results the influence on the flywheel vibration and the generated disturbance torque. This means that there is a coupling effect in the CMG. In this article, we focused on this coupling relationship between the flywheel vibration and the gimbal rotation in a single gimbal control moment gyroscope (SGCMG) system. Firstly, a vibration model of the flywheel with variable stiffness supporting is established. And the rotation model of the gimbal is also developed. The flywheel model and the gimbal model are coupled with each other through the variable stiffness supporting and gyroscope effect. Based on the numerical simulations the interactions among the bearing stiffness, the flywheel vibration and the gimbal rotation are analyzed. Finally, experiments are carried out on the prototype. The experimental results have verified the theoretical analysis and the simulations, and which would support the design of high-performance control system.

Indirect Measurement of Rotor Dynamic Imbalance for Control Moment Gyroscopes via Gimbal Disturbance Observer.

The high-precision speed control of gimbal servo systems is the key to generating high-precision torque for control moment gyroscopes (CMGs) in spacecrafts. However, the control performance of gimbal servo systems may be degraded significantly by disturbances, especially a dynamic imbalance disturbance with the same frequency as the high-speed rotor. For assembled CMGs, it is very difficult to measure the rotor imbalance directly by using a dynamic balancing machine. In this paper, a gimbal disturbance observer is proposed to estimate the dynamic imbalance of the rotor assembled in the CMG. First, a third-order dynamical system is established to describe the disturbance dynamics of the gimbal servo system, in which the rotor dynamic imbalance torque along the gimbal axis and the other disturbances are modeled to be periodic and bounded, respectively. Then, the gimbal disturbance observer is designed for the third-order dynamical system by using the total disturbance as a virtual measurement. Since the virtual measurement is derived from the inverse dynamics of the gimbal servo system, the information of the rotor dynamic imbalance can be obtained indirectly only using the measurements of gimbal speed and three-phase currents. Semi-physical experimental results demonstrate the effectiveness of the observer by using a CMG simulator.

High-Precision Speed Control Based on Multiple Phase-Shift Resonant Controllers for Gimbal System in MSCMG

The high precision speed control of gimbal servo system in magnetically suspended control moment gyro (MSCMG) suffers from periodic torque disturbances, which lead to periodic fluctuations in speed control. This paper proposes a novel multiple phase-shift resonant controller (MPRC) for a gimbal servo system to suppress the periodic torque ripples whose frequencies vary with the operational speed of the gimbal servo motor and high-speed motor. First, the periodic torque ripples caused by cogging torque, flux harmonics and the dynamic unbalance of the high speed rotor are analyzed. Second, the principle and structure of MPRC parallel with proportional integral (PI) controllers are discussed. The design and stability analysis of the proposed MPRC plus PI control scheme are given both for the current loop and speed loop. The closed-loop stability is ensured by adjusting the phase in the entire operational speed range. Finally, the effectiveness of the proposed control method is verified through simulation and experimental results.