Control Moment Gyros Research Articles

Integrated design of a lightweight metastructure for broadband vibration isolation

Quasi-zero stiffness (QZS) isolators have demonstrated appropriate low-frequency vibration isolation performance without sacrificing the load-bearing capacity. The current ‘combined’ design of QZS isolators, however, suffers from complex mechanisms and cumbersome assembly, requiring the parallel arrangement of both negative-stiffness and positive-stiffness elements. Inspired by the multi-functional integration ability of metastructure, this study explores a lightweight design of three-dimensional (3D) QZS metastructure with ‘monolithic’ beam-like unit cells. The study begins with the optimization design method to reach customizable QZS features in the vibration isolation metastructure for complex working environments. Then, it turns to rapid manufacturing to fabricate the metastructure prototypes, whose static and vibration test results demonstrate good agreements with the analytical and numerical results. In an experiment for the vibration isolation of a typical control moment gyro (CMG) of spacecraft, the QZS metastructure exhibited excellent vibration isolation performance (up to 90% reduction in 100–600 Hz frequency range) with only a 4.5% gain in mass. As such, the proposed 3D QZS metastructure paves a new way to the design of lightweight, compact and broadband vibration isolators.

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.

Equilibrium space and a pseudo linearization of nonlinear systems

This paper attempts to extend the concept of the equilibrium point to what is called equilibrium space, which can adapt to a system in which there exists an infinite number of equilibrium points. In the context of Lyapunov’s linearization method extended for the equilibrium space, this paper proposes a pseudo linearization, from which we can derive a linear representation for a nonlinear system. The equilibrium state of this pseudo linearization and its stability are shown to be the same as that of the original nonlinear system. As an example of the applicability, the proposed pseudo linearization is applied to derive a discrete-time model for a control moment gyroscope system from a nonlinear continuous-time model. Simulation results show that the discrete-time model derived using the proposed pseudo linearization yields responses that are closer to that of the continuous-time model than the discrete-time model derived by the well-known forward-difference method and the conventional pseudo linear representation method, even with a large sampling interval.

Micro-vibration modeling and analysis of single-gimbal control moment gyros

Micro-vibration modeling and analysis of single-gimbal control moment gyros (SGCMGs) are conducted in this study. Considering the rotation and support effect of the low-speed gimbal, a nonlinear time-varying dynamic model for micro-vibration analysis of an SGCMG is established using the energy theorem. By considering the Hertzian contact, elastohydrodynamic lubrication, and surface waviness, the nonlinear supporting forces and moments of the angular contact ball bearings on the high-speed rotor and low-speed gimbal are derived, and accordingly, an iterative solution method is proposed. Based on a three-axis dynamic force measurement platform, the dynamic characteristics of a real SGCMG are tested to verify the rationality of the proposed micro-vibration model. Subsequently, the effects of unbalance mass, surface waviness amplitude, gimbal lock angle, and rotation angular speed of the gimbal on the three-axis gimbal bearing transmission forces are discussed. The findings of this study provide insights for clarifying the micro-vibration characteristics and provide a theoretical basis for the working state design and structural optimization of SGCMGs.

Satellite Attitude Control Using Double-Gimbal Variable-Speed Control Moment Gyro with Unbalanced Rotor

Attitude dynamics of a rigid satellite actuated using a double-gimbal variable-speed control moment gyro (DGVSCMG) with an unbalanced rotor is derived in the framework of geometric mechanics. The proposed formulation accounts for dynamics of the gimbal motors and the rotor motor for finding the required motor torque to actuate the satellite along with the DGVSCMG for achieving high-precision attitude control. The satellite attitude control is accomplished using a proposed cascaded adaptive fixed-time sliding mode control to ensure bounded finite-time convergence. A sliding manifold is also designed to ensure convergence of gimbals angular rates to the desired values. Actuator saturation, system uncertainties such as intrinsic disturbance torques due to the gimbals and rotor bearing friction, extrinsic disturbances due to the environmental factors, and uncertainty in inertia of the satellite bus are accounted for designing the controller. Lyapunov stability analysis is carried out to prove bounded finite-time stability of the proposed system. Simulation results are presented to substantiate the claim made assuming the rigid satellite to be equipped with only one DGVSCMG.

Cover Image

The cover image is based on the Research Article Efficient learning of robust quadruped bounding using pretrained neural networks by Zhicheng Wang et al., https://doi.org/10.1049/csy2.12062. and Original Article Disturbance rejection for biped robots during walking and running using control moment gyroscopes by Haochen Xu et al., https://doi.org/10.1049/csy2.12070.

Backstepping-Based Steering Control for Spacecraft Attitude Control Using Two-Skewed Control Moment Gyroscopes

Numerous control methods that use two reaction wheels have been proposed for the underactuated control problem. However, few studies have applied two single-gimbal control moment gyroscopes (SGCMGs) to the three-axis attitude control problem. In this study, under the assumption that the total initial angular momentum is zero, a steering control law for the three-axis attitude maneuvers of a spacecraft with an array of two-skewed SGCMGs is designed using the backstepping technique without setting a constraint on the range of gimbal angles. The spacecraft attitude is expressed in terms of the parameters, which are suitable for the underactuated attitude control problem. The control gains are appropriately chosen to guarantee controller stability. The proposed steering control law is validated through numerical simulations. The results show that the proposed steering control law can achieve a shorter settling time than that obtained from a control law with a constraint on the range of gimbal angles.

Formula omitted] gain-scheduled state-feedback design with experimental validation in a control moment gyroscope represented as a polynomial LPV model

The main contribution of this paper is a new H2 gain-scheduled state-feedback synthesis condition for continuous-time linear parameter-varying (LPV) systems where the parameters have bounded rates of variation. The matrices of the model as well as the control gain can have arbitrary polynomial dependence on the time-varying parameters. The synthesis conditions are formulated in terms of LMI relaxations combined with a search in a bounded scalar parameter, which can be used to obtain controllers with improved performance. As an experimental validation of the results, gain-scheduled controllers are designed and applied to a control moment gyroscope modeled as an LPV system with polynomial dependence on the time-varying parameters. Comparisons with a time-invariant controller, designed with the same performance criterion, are presented to illustrate the advantages of the proposed approach.

Neural-Network-Based Terminal Sliding Mode Control of Space Robot Actuated by Control Moment Gyros

This paper studies the trajectory tracking control of a space robot system (SRS) in the presence of the lumped uncertainties with no prior knowledge of their upper bound. Although some related control methods have been proposed, most of them have either not been applied to SRSs or lack rigorous stability proof. Therefore, it is still a challenge to achieve high accuracy and rigorous theoretical proof for tracking control of SRSs. This paper proposes a new integrated neural network- based control scheme for the trajectory tracking of a SRS actuated by control moment gyros (CMGs). A new adaptive non-singular terminal sliding mode (ANTSM) control method is developed based on an improved radial basis function neural network (RBFNN). In the control method, a new weight update law is proposed to learn the upper bound of the lumped uncertainties. With the advantages of RBFNN and ANTSM, the controller has high control accuracy, fast learning speed and finite-time convergence. Different from most on-ground robotic manipulator controllers, a kinematic controller with position and attitude control laws is also designed for the satellite platform to remain stable. The stability of the closed-loop system is proved by the Lyapunov method with a high mathematical standard. Comparative simulation results demonstrate the effectiveness of the proposed control scheme with preferable performance and robustness.

Disturbance rejection for biped robots during walking and running using control moment gyroscopes

AbstractKeeping balance in movement is an important premise for biped robots to complete various tasks. Now, the balance control of biped robots mainly depends on the cooperation of various joints of the robot's body. When robots move faster, the adjustment allowance of joints is reduced, and the robot's anti‐disturbance ability will inevitably decline. To solve this problem, the control moment gyroscope (CMG) is creatively used as an auxiliary stabilisation device for fully actuated biped robots and the CMG assistance strategy, which can be integrated into the biped's balance control framework, is proposed. This strategy includes model predictive control module, distribution module, and CMG precession controller. Under the command of it, CMGs can effectively assist the robot in resisting impact and returning to initial positions in time. The results of anti‐impact simulation on the walking and running biped robot prove that, with the help of CMGs, the robot's ability to resist disturbance and remain stable is significantly improved.The cover image is based on the Original Article Disturbance rejection for biped robots during walking and running using control moment gyroscopes by Haochen Xu et al., https://doi.org/10.1049/csy2.12070.

Steering Law for Control Moment Gyroscopes with Online Torque Capacity Maximization

While single-gimbal control moment gyroscopes (CMGs) remain the actuators of choice for agile spacecraft, using over-redundant or overdesigned CMG arrays will cease to be a viable approach as agility requirements increase. The torque envelope of a CMG array under gimbal rate constraints is a zonotope, whose geometrical characteristics can be used to systematically increase the torque capacity around an arbitrarily given axis. For a four-CMG roof array, which consists of two coplanar CMG pairs, the torque capacity is a function of the allocation of angular momentum between the pairs. Based on the latter, a gimbal angle steering law is developed that maximizes the CMG array’s torque capacity around a preferred axis defined by the current slew maneuver. A main feature of the proposed steering law is that this maximization does not require offline computations for any given preferred axis. In addition, an angular-momentum-based attitude tracking control law is formulated. As verified in numerical simulations, the developed steering and attitude control algorithms are able to follow a typical agile reference profile with adequate time domain performance while satisfying actuator constraints.

Frequency Response Data-Based LPV Controller Synthesis Applied to a Control Moment Gyroscope

Control of systems with operating condition-dependent dynamics, including control moment gyroscopes (CMGs), often requires operating condition-dependent controllers to achieve high control performance. The aim of this brief is to develop a frequency response data-driven linear parameter-varying (LPV) control design approach for single-input single-output (SISO) systems, which allows improved performance for a CMG. A stability theory using a closed-loop frequency response function (FRF) data is developed, which is subsequently used in a synthesis procedure that guarantees local stability and performance. Experimental results on a CMG demonstrate the performance improvements.

Design, optimization and test of RHMB considering dynamic characteristics

The coil inductance, stiffness and losses of the magnetic bearing (MB) have great influence on the dynamic performance for the magnetically suspended control moment gyro (MSCMG) application. Based on the equivalent magnetic circuits considering flux leakage effects, a design, optimization and test method is proposed to enhance the dynamic response ability for the radial hybrid MB (RHMB). The optimization design objectives including bearing force, stiffness, coil current, mass, inductance and loss estimation are discussed under the multiple constraints. Compared with the original design, the dynamic characteristics including frequency responses of current and rotor displacements for the RHMB-rotor system are significantly improved after optimization. A prototype of MSCMG is fabricated to verify the dynamic response characteristic of the RHMB.

미소진동 대응 Stewart Platform 기반 Hexapod형 진동절연장치의 배치에 따른 전달률 특성 연구

A microvibration source such as a reaction wheel or control moment gyro, which adversely affects the high pointing stability required for modern satellites, generates a six-degrees-of-freedom (6-DOF) disturbance force. Therefore, the vibration isolator must also be capable of isolating 6-DOF vibration. A hexapod isolator is designed to isolate 6-DOF vibration by extending the single-axis isolator. The Stewart platform is widely used for 6-DOF vibration isolation and manipulation. The cubic configuration, which is one of the representative configurations of the Stewart platform, has several advantages in terms of manipulation; however, there is a cross-coupling issue in terms of vibration isolation. In this study, for the generalized configuration of the Stewart platform, force transmissibility change due to the varying angle of the strut and strut inclination angle is analyzed to suggest the optimal configuration based on the Stewart platform to reduce cross-coupling for a 6-DOF microvibration isolator.

Design, analysis and implementation of control moment gyroscope (CMG) mechanism to self-balance a moped bike

This paper presents the design and implementation of the control moment gyroscope (CMG) mechanism on the Okinawa IPRAISE Scooter, an electric moped, to self-balance it with or without a rider. The scooter can be balanced in static as well as in moving condition so that it won’t fall over. Higher torque amplification and momentum storage capacity makes CMG superior over other mechanisms like reaction wheel, mass balancing, controlling the movement of front steering, etc. CMG mechanism consists of a pair of spinning discs, i.e., flywheels which are driven continuously by DC motors about vertical z-axis. An encoder deployed to sense the tilt angle about longitudinal y-axis provides feedback to the PID controller. The controller, in turn, produces restoring torque by gimbal action with the help of a pair of stepper motors mounted on horizontal x-axis to maintain the scooter in vertical position. Thus, using gyroscopic effect of two spinning flywheels, CMG mechanism generates reactive torque which assist the user to balance the bike in several riding modes. Stack up calculations were performed to make a tradeoff between moment of inertia and mass of flywheels to arrive at the dimensions of the flywheel. Subsequently, 3D model of the mechanism is developed with the help of CREO. The mechanism is analyzed and simulated in ANSYS. Mock-up samples were procured. It is then mounted on the scooter and tested. One optimum location is finalized based on the center of gravity. Finally, the bike is found to balance itself resulting in a compact and robust mechanism giving safe and comfortable ride. This, however, comes at an additional ten percent power consumption, twenty-five percent increase in weight and nine percent increase in cost. Further improvement can be done by reducing this parameters by using lighter materials and small size motors.

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.

Synchronous Vibration Moment Suppression for AMBs Rotor System in Control Moment Gyros Considering Rotor Dynamic Unbalance

In rotating machinery, the rotor mass unbalance will cause synchronous vibration, in which static unbalance will produce synchronous vibration force, and dynamic unbalance will produce synchronous vibration moment. In order to suppress the vibration moment of the magnetically suspended control moment gyro, a modified dual-channel notch filter (DNF) is proposed in this article. First, the modeling of the rotor system with mass unbalance is performed. Then, the design of modified DNF is carried out. This notch filter uses the equivalent vibration moment calculated by the current and displacement signals as input, and uses the orthogonal characteristics of the moment signals in the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Y</i> directions to enter the controller at the same time. The stability of the rotor system with a DNF is proven. Finally, the experimental results are given to show that this method can effectively eliminate the synchronous vibration moment in the rotor system.

Oscillation Control of Two-Wheeled Robot using a Gyrostabilizer

Two-wheeled robots are popular in transportation applications because of their high maneuverability. In this research, the oscillation attenuation performance of the control moment gyroscope (CMG) for the two-wheeled robot was studied. The stored kinetic energy of a CMG can offer a weight and volume saving compared to conventional vibration absorbers. This CMG is also more reactionless than other conventional absorbers by transforming the impact of angular momentum to unidirectional thrust along the center of gravity. The gimbals can precess while providing the angular momentum under the gravitational force. This study indicated that the CMG can operate in a wide range of excitation frequencies to balance the robot in a stable period. Because the flywheel speed is much easier changed to thrust against the unwanted oscillations disturbing the robot stability. There is a relation between the gimbal amplitude and the flywheel speed of CMG, in which the required flywheel speed can be reduced if the higher gimbal amplitude is chosen. It can be also concluded from the study that the oscillation amplitudes at the target frequency can decrease as much as flywheel speed increases. There was also a mathematical model using ANSYS software. The simulation results using ANSYS matched well with the theoretical results of the Lagrangian model.