Control Moment Gyros Research Articles

CMG-based anthropomorphic test device for human rider behavior reproduction for two-wheeled self-balancing personal mobility

With the expansion of the self-balancing personal mobility (SBPM) market, an increasing number of accidents have been reported in recent years, while the relevant safety regulations have not been established yet. Safety and dynamic stability of the SBPM is critical for their operation, and they must be evaluated for them. SBPMs are operated by a human rider even for the evaluation tests, so the objectivity and the repeatability of the tests cannot be ensured. Also, there could even be a safety issue with the test rider. To solve this problem, we propose an anthropomorphic test device (ATD), which is a type of dummy robot. The ATD reproduces the human rider's dynamic behavior using a control moment gyroscope (CMG), so it can drive the SBPM instead of a human rider for the evaluation tests. Just like a human rider controls the SBPM by the disturbance torque made by the posture (i.e. the center of gravity) change, the CMG-based ATD reproduces the dynamic behavior of the SBPM by creating the same disturbance torque using the CMG. A detailed working principle and the design of the CMG-based ATD is introduced in this paper. For the validation of the CMG-based ATD's human rider behavior reproduction performance, the dynamic behavior of the SBPM measured from the actual human ride is compared with the data from the computer simulations.

Integrated control of attitude maneuver and vibration suppression of flexible spacecraft based on magnetically suspended control moment gyros

This paper adopts magnetically suspended control moment gyro (MSCMG) to realize the integration of attitude control and wideband micro-vibration suppression of spacecraft without adding extra hardware resources. The coupling between central rigid body and flexible attachment has been effectively retained in the controller design. First, an open-loop modal observer is constructed in advantage of the inherent physical characteristics of flexible modes, and then an adaptive backstepping controller involving flexible modal estimation, spacecraft attitude quaternion, and angular velocity is designed. Next, the band-pass filters are employed to separate the low-frequency gimbal command angular rate signal and medium–high-frequency rotor command angular rate signal, respectively, so that MSCMG can accurately track the command signal output by the integrated controller. Taking advantage of MSCMG’s ability to output high bandwidth micro-gimbal moment, the proposed method can not only meet the requirement of spacecraft rapid maneuver but also effectively suppress the broadband micro-vibration, including low-frequency flexible vibration and medium–high-frequency micro-vibration caused by spacecraft rotating parts. Numerical simulations and frequency domain analysis demonstrate the correctness and effectiveness of the proposed method.

A performance study of a wearable balance assistance device consisting of scissored-pair control moment gyroscopes and a two-axis inclination sensor

Excessive postural sway while standing can lead to falls and injuries. A designed wearable balance assistance device which consists of scissored-pair control moment gyroscopes and a two-axis inclination sensor is introduced to reduce fall risk from excessive sway among the elderly. The prototype has dimensions of H50cm × W44cm × D30cm and weighs 15.03 kg. This study aims to investigate the effects of generated torque of the prototype on human subjects and aims to determine if the two-axis inclination sensor can detect sway amplitude and sway direction during an occurrence of excessive sway. Two healthy male subjects participated in the study. According to the results, the detected body incline angle related to the acquired sway amplitude of COP trajectories with correlation factors of 0.92 and 0.88 for the two subjects. The detected sway angle related to the acquired sway direction of COP trajectories with the correlation factors of 0.99 and 0.98 for the two subjects. The maximum-allowable generated torque of the prototype with an assigned actuating angle varying within ±15.6° from the acquired sway direction of COP trajectories was able to drive the COP of 60-kilogram-weighted healthy subject maintaining balance at posterolateral limits of stability with an average body incline angle of 5.74° to pass his standing secure zone. The results indicate that the prototype has the potential of being a wearable balance assistance device which can reduce fall risk from excessive sway among the elderly; however, some improvements are still required in regards to shape, size, mass, generated torque, and strength.

Using gyro stabilizer for active anti-rollover control of articulated wheeled loader vehicles

Articulated wheeled loader vehicles have frequent rollover accidents as they operate in the complex outdoor environments. This article proposes an active anti-rollover control method based on a set of single-frame control moment gyro stabilizer installed on the rear body of the vehicle. The rollover dynamic model is first established for articulated wheeled loader vehicle with gyro stabilizer. The proposed control strategy is then applied in simulation to verify the rollover control effect on the vehicle under steady-state circumferential conditions. Finally, a home-built articulated wheel loader vehicle with gyro stabilizer is used to further verify the proposed control strategy. The results show that the vehicle can quickly return to the stable driving state and effectively avoid the vehicle rollover when a suitable anti-roll control moment can be provided by the gyro stabilizer. As a result, the articulated wheeled loader vehicle is able to operate safely in a complex outdoor environment.

Dynamics modeling and attitude stabilization control of a multiarmed space robot for on-orbit servicing

With the number of large-scale facilities, malfunctioning spacecraft, and debris expected to increase in space, on-orbit servicing, including assembly, monitoring, maintenance, refueling and deorbiting, has become a major concern in space missions. Space robots can efficiently cope with a large number of on-orbit servicing missions while avoiding the high risks and reducing costs of extravehicular activity. The challenges of space robots with multiple arms include the complex dynamics and the coupling between the floating base and the end-effector. To handle these problems, a dynamics model with topological structure is firstly established for a four-arm space robot based on the kinematic chain symbolic calculus system and Axis-Invariants, which have the benefits of iterative structure and can avoid complex derivation of traditional dynamics modeling methods. Then, an attitude stabilization strategy consisting of improved nonlinear model predictive control and a hybrid actuator is implemented to handle the disturbance generated by the manipulation of multiple robot arms. The hybrid actuator can provide accurate control torque while simultaneously avoiding the singularity and saturation of the control moment gyro and reaction wheel, respectively. Finally, a scenario of space debris recycling is used to demonstrate the effectiveness of the proposed modeling and control strategy for on-orbit servicing missions with multiarmed space robots.

Stable control of the high-speeding magnetically suspended rotor based on extended state observer and two-degree freedom internal model control for control moment gyros with serious moving-gimbal effects

For a magnetically suspended control moment gyro (MSCMG), which is an ideal attitude actuator for its large outputting control moment and fast response, the moving-gimbal effects due to the coupling between the moving gimbal and high-speeding rotor will make the magnetically suspended rotor (MSR) unstable. To improve control precision, both the dynamic model of MSR and the feedback linearization control are done to decouple tilting motion, and poles of the system are reconfigured to reduce control error. To suppress the varying disturbance moments caused by moving-gimbal effects, an extended state observer (ESO) is originally designed to estimate and compensate them timely and accurately. To improve system robustness, a two-degree freedom internal model control (2-DOF IMC) is researched to suppress model error. Compared with existing proportional integral derivative (PID) control method, simulations done on a single gimbal MSCMG with 200 N.m.s angular momentum indicated that this presented control method with ESO and 2-DOF IMC can suppress the moving-gimbal effects more effectively and make the rotor suspension more stable.

Steering control law for double-gimbal scissored-pair CMG

Because control moment gyroscopes (CMGs) can generate a large torque compared to reaction wheels, they are used as actuators for attitude control of large spacecraft. However, when the number of Single-Gimbal CMG (SGCMG) units is five or less, there can be internal singularities that cannot generate torque around the desired direction. To construct a system that has no internal singularities, six or more SGCMGs are required, because an orthogonally arrayed, three scissored-pair CMG system has no internal singularities. Because CMG singularities are disruptive for attitude control, a great deal of effort has been devoted to overcoming the CMG singularity problem; the various designs include Variable-Speed CMGs (VSCMGs), Double-Gimbal CMGs (DGCMGs), and Double-Gimbal Variable-Speed CMGs (DGVSCMGs). However, these designs still have problems, such as a slow response to torque generation commands about the wheel axis in VSCMGs and DGVSCMGs, and difficulty in precise attitude tracking when perturbation torque is generated to avoid singularities. To overcome the problems of the traditional CMG configurations, this paper proposes a new CMG system configuration that we call the Double-Gimbal Scissored-pair CMG (DGSPCMG) system. Because the DGSPCMG system is a hybrid system combining a Scissored-Pair CMG and a DGCMG, the DGSPCMG system does not have internal singularities except at the origin and along the x-axis. Moreover, this system can recover from an internal singularity by null motion only, and from outer singularities (saturation singularities) by steering the scissored-pair gimbals only. Thus, generation of perturbation torque is unnecessary for recovering from singularities, and a precise attitude tracking maneuver can be more easily achieved. This paper presents a conceptual design of a DGSPCMG system and describes a steering control law for the proposed system. Furthermore, the validity of the proposed steering control law is demonstrated through numerical simulations and results of comparison experiments are shown to demonstrate the advantage of the DGSPCMG over a VSCMG.

Stabilization and disturbance attenuation control of the gyroscopic inverted pendulum

In this study, a control moment gyroscope is used as an actuator to stabilize the inverted pendulum. A control strategy is proposed to stabilize the inverted pendulum at the upright unstable equilibrium point and to maintain the gimbal angle as small as possible. Such a problem is formulated as a constrained H∞ disturbance attenuation problem and then transformed into solving linear matrix inequalities. The performance of the proposed controller is evaluated through simulation for linear and nonlinear cases. It is shown that the proposed state-feedback control strategy effectively stabilizes the inverted pendulum.

Design and Structural Analysis of a Control Moment Gyroscope (CMG) Actuator for CubeSats

Following a global trend towards miniaturization, the population of nano- and micro-satellite continues to increase. CubeSats are standardized small size satellites based on 10 × 10 × 10 cm cube modules (1U) and are becoming sophisticated platforms despite their very small size. This paper details the design and the structural analysis of a Control Moment Gyroscope (CMG) actuator for agile CubeSats with a physical size up to 12U, which require high torque actuators. CMGs have inherited torque amplification capabilities and the recent advances in motor miniaturization make them ideal candidates for small satellite missions with slew rate requirements. The system’s requirements are derived based on conceptual agility requirements for an agile (highly maneuverable) CubeSat which needs to achieve a 90° maneuver in 90 s. With specific cost, mass and volume requirements, the proposed CMG design is based on some of the smallest available off-the-shelf electric motors and uses a light aluminum casing design. The proposed design uses stepper motors for the gimbal mechanism as a low cost, compact and low power solution, contributing to an overall low mass of the full CMG cluster. Static and dynamic analyses were performed to assess the mechanical integrity of the system for launch loads. Apart from a necessary custom control electronic board, the complete mechanical assembly has been designed including electrical hardware. Analyses demonstrate that the overall stress levels acting on the system are manageable by the CMG design. Bolted joints are critical and should be studied independently as the chosen model created singularities around these areas. Each individual CMG of the designed pyramidal cluster is shown to weigh about 35 g. Using the proposed CMG design with a customized avionics board, the complete CMG system is shown to weigh 250 g and occupies slightly more than ½U volume for a CubeSat, indicating the feasibility of CMGs for agile CubeSats.

Attitude control for spacecraft using pyramid-type variable-speed control moment gyros

In this paper, the attitude control of spacecraft using a pyramid-type variable-speed control moment gyro (VSCMG) system is considered. For successive attitude maneuvers, it is desirable that the wheel angular momentums are regulated to nominal values after an attitude maneuver. In addition, avoidance of reference aligned singularity (RAS) is also important. RAS is a singularity point where the singular direction of the constant-speed control moment gyro (CSCMG) system is aligned to a reference torque. Regarding the motivations, this paper proposes a steering law which achieves attitude control and regulates the wheel angular momentums while successfully avoiding RAS. Both numerical simulations and experimental verification are performed to demonstrate not only the validity of the proposed method, but also a certain robustness against unmodeled dynamics and the gravity torque.

Robust trajectory tracking control of an underactuated control moment gyroscope via neural network–based feedback linearization

In this document, an underactuated two degrees–of–freedom control moment gyroscope (CMG) is studied. Specifically, the problem of trajectory tracking in the non-actuated joint is addressed. The feedback linearization technique is used to design a model-based controller. Then, an adaptive neural network–based scheme is designed to add robustness with respect to model uncertainties. Studies on the internal and output dynamics are presented. The introduced theory is validated by means of real–time experiments. The comparisons among a linear controller, a cascaded PID–PID scheme, and a known adaptive neural network controller are presented to assess the performance of the novel robust controller given in this work. Better tracking accuracy is obtained with the introduced approach.

Fault modeling of general momentum exchange devices in spacecraft attitude control systems

This paper investigates the mechanism of various faults in momentum exchange devices. These devices are modeled as a cascade electric motor (EM) - variable speed drive(VSD) system. Considering the mechanical part of the EM and the VSD system, potential faults are reviewed and summarized. Then, a general fault model in a cascade multiplicative structure is established for momentum exchange devices. Based on this general model, various fault scenarios can be simulated and tested, and the possible outputs affected by faults can be appropriately visualized. Specifically, six types of working condition are identified, and the corresponding fault models are constructed. Using these fault models, the control responses using reaction wheels and single gimbal control moment gyros under various fault conditions can be demonstrated. The simulation results show the severities of the faults and demonstrate that the additive fault is more serious than the multiplicative fault from the viewpoint of control accuracy. Finally, existing fault-tolerant control strategies are briefly summarized and potential approaches including both passive and active ones accommodating gimbal fault of single gimbal control moment gyro are demonstrated.

Whirl Mode Suppression for AMB-Rotor Systems in Control Moment Gyros Considering Significant Gyroscopic Effects

For a magnetically suspended control moment gyroscope with strong gyroscopic effects, the whirl mode (nutation and precession) stability control of the active magnetic bearing (AMB) rotor system has always been a challenging problem. This article proposes a robust control method combined with regional pole assignment to achieve the stability control of the whirl mode in the AMB-rotor system. First, the physical model of multi-degree-of-freedom magnetic bearing system is analyzed in detail, and the state-space model of the system is established. Then, the gyroscopic effects varying with the rotor speed are considered as a bounded parameter perturbation of the system, and the constraints on the controller to achieve the system stability are obtained. Furthermore, in order to increase the system stability margin and the whirl mode damping, the additional constraints on the controller are derived through the regional pole assignment method. Finally, all constraints are converted into the form of linear matrix inequalities (LMIs), and a controller satisfying all the constraints can be obtained by solving the LMIs. Experimental results demonstrate that the designed robust controller can achieve the stability control of nutation and precession as well as keeping a satisfactory system performance.

Development of a single-wheeled inverted pendulum robot capable of climbing stairs

ABSTRACTIn this paper, we propose the design of a single-wheeled robot capable of climbing stairs. The robot is equipped with the proposed climbing mechanism, which enables it to climb stairs. The mechanism has an extremely simple structure, comprised of a parallel arm, belt, harmonic drive, and pulley. The proposed climbing mechanism has the advantage of not requiring an additional actuator because it can be driven by using a single actuator that drives the wheel. The robot is equipped with a control moment gyroscope to control the stability in a lateral direction. Experimental results demonstrate that the robot can climb stairs with a riser height of 12–13 cm and a tread depth of 39 cm at an approximate rate of 2 to 3 s for each step.

Integration planning of gimbal angle and attitude motion for zero propellant maneuver under attitude and control moment gyroscope constraints

Zero propellant maneuver is an advanced concept of large spacecraft attitude control that has recently been applied to International Space Station. The objective of this paper is the zero propellant maneuver path planning of space station under attitude and control moment gyroscope constraints. First, a multi-constraint model of zero propellant maneuver with single gimbal control moment gyroscopes is established. Then, an integrated planning algorithm of gimbal angle and attitude motion is proposed: Local Control Differential Evolution. The algorithm can simultaneously handle attitude constraints and control moment gyroscope constraints to obtain an attitude path that satisfies the attitude constraints and a gimbal angle path that is far from singularity and saturation. In addition, the algorithm combines the local control algorithm with the global differential evolution algorithm. The local control algorithm based on the potential function idea can better deal with local attitude obstacle constraints, and the global optimization algorithm based on the improved differential evolution algorithm can perform global gimbal angle optimization. Finally, simulation results show that the method is effective in dealing with both attitude and control moment gyroscope constraints.

Posture stability control of a small inverted pendulum robot in trajectory tracking using a control moment gyro

ABSTRACTThis paper reports on a posture stability control method for an inverted pendulum robot using a control moment gyro (CMG) mounted on the top of the inverted pendulum. As an inverted pendulum dimension decreases, a time to fall over to an angle where an inverted pendulum cannot restore its posture becomes shorter; however, a small inverted pendulum robot cannot have a powerful computer because of space limitations. This means it requires a faster and smaller way to maintain its balance. Furthermore, inverted pendulum robots require movement space to gain a restoring force to keep their balance. We thus proposed an inverted pendulum robot using a CMG to obtain the necessary restoring force. The CMG’s effects decreased the robot’s falling over speed, meaning it can keep its balance without moving. We successfully demonstrated that an inverted pendulum robot with a CMG can separate posture stability control and trajectory tracking control. The validity of the inverted pendulum robot with a CMG was confirmed comparing the two experiments. In the first experiment, the CMG performed posture stabilization and the wheel performed trajectory tracking. In the second experiment, only the wheel performed posture stabilization and trajectory tracking.

An Automatic Bearing Fault Diagnosis Method Based on Characteristics Frequency Ratio.

Bearing is a key component of satellite inertia actuators such as moment wheel assemblies (MWAs) and control moment gyros (CMGs), and its operating state is directly related to the performance and service life of satellites. However, because of the complexity of the vibration frequency components of satellite bearing assemblies and the small loading, normal running bearings normally present similar fault characteristics in long-term ground life experiments, which makes it difficult to judge the bearing fault status. This paper proposes an automatic fault diagnosis method for bearings based on a presented indicator called the characteristic frequency ratio. First, the vibration signals of various MWAs were picked up by the bearing vibration test. Then, the improved ensemble empirical mode decomposition (EEMD) method was introduced to demodulate the envelope of the bearing signals, and the fault characteristic frequencies of the vibration signals were acquired. Based on this, the characteristic frequency ratio for fault identification was defined, and a method for determining the threshold of fault judgment was further proposed. Finally, an automatic diagnosis process was proposed and verified by using different bearing fault data. The results show that the presented method is feasible and effective for automatic monitoring and diagnosis of bearing faults.

Calibration, Compensation and Accuracy Analysis of Circular Grating Used in Single Gimbal Control Moment Gyroscope.

The accuracy of the circular grating is the key point for control precision of the single gimbal control moment gyroscope servo system used in civilian micro-agile satellites. Instead of using the multi reading heads to eliminate eccentricity errors, an algorithm compensation method based on a calibration experiment using a single reading head was proposed to realize a low-cost and high accuracy angular position measurement. Moreover, the traditional hardware compensation method using double reading heads was also developed for comparison. Firstly, the single gimbal control moment gyroscope system of satellites was introduced. Then, the errors caused by the installation of the reading head were studied and the mathematic models of these errors were developed. In order to construct the compensation function, a calibration experiment using the autocollimator and 24-sided prism was performed. Comparison of angle error compensation using the algorithm and hardware method was presented, and results showed that the algorithm compensation method proposed by this paper achieved the same accuracy level as the hardware method. Finally, the proposed method was further verified through a control system simulation.

Controlling a Satellite using Single-Gimbal Control Moment Gyroscope During Their Spinning and Braking

The capabilities of using single-gimbal control moment gyroscopes (CMGs) for the attitude control of Earth remote sensing (ERS) satellites are studied. The situation of the incomplete spinning of CMGs used for controlling the angular motion of the satellite when these gyros have a different angular momentum is considered. Control algorithms that can be applied in this situation are proposed, and it is shown that they can be used to stabilize the satellite. Using simulation, it is shown that a satellite’s angular motion can be controlled by CMGs having different angular momenta.

Synchronous vibration control for magnetically suspended control moment gyros using optimal notch filter

The synchronous vibration in magnetically suspended control moment gyros is a common problem due to unavoidable rotor mass imbalance. This work proposes an optimal notch filter for suppressing the synchronous vibration force. The synchronous vibration force is firstly modelled, and the preliminary design of phase-shift notch filter is given to ensure the system stability. Then the optimal phase of notch filter is discussed, and its theoretical expression is given. Finally, simulation results illustrate the superiority of the notch filter with optimal phase, and experimental results verify the effectiveness of optimal notch filter.