Three-axis Control Research Articles

Embedded Star Catalog Calculation Tool for Autonomous Star Trackers

Autonomous star trackers are crucial attitude sensors for spacecraft three-axis control. They are the most accurate commercial-off-the-shelf sensors available. An autonomous star tracker is an optoelectronic device that autonomously determines the spacecraft’s attitude, using an embedded star catalog that is compared to in-orbit images to perform stellar field recognition. This work presents a computational tool to calculate the embedded star catalog for any specified star sensor. To optimize the star sensor design, the tool developed provides users with sensor accuracy analysis regarding the observed starfield.

Advanced Servo Control and AI Integration in 3-DoF Platforms for Enhanced Simulation Interactivity

This paper proposes a new approach to enhance the realism and interactivity of shooting simulation systems by integrating a three-degree–of–freedom (3-DoF) platform with sensory and interactive elements, as well as digital content. The system employs visual effects computers and servo controls, utilizing network packet messages for communication based on different scene definitions. When the control handle sends commands, the visual effects computer transmits control parameters to the image generator. Additionally, AI-controlled aircrafts act as enemy planes, autonomously determining flight paths, tracking targets, and engaging in combat, thereby enhancing realism in interactive mechanisms. An iterative learning control (ILC) is designed to provide the platform with good dynamic response, load capacity, and tracking ability when operated by a manual control handle. The core control uses a TMS320F28377D digital signal processor from Texas Instruments, integrated with visual effects computers for three-axis control, controller computation, finite state machines, and network communication operations. Experimental results demonstrate the feasibility and effectiveness of the developed three-axis shooting platform, achieving immersion and coordination with AI enemy aircrafts.

Design of submarine pipeline inspection system based on ultrasound

A design of a non-destructive testing system for underwater pipelines based on ultrasound has been proposed, consisting of a three-axis control system and an ultrasonic thickness measurement system. This can achieve full coverage testing and real-time data transmission of pipeline wall thickness through integrated composite rotating mechanisms, travel driving mechanisms, pipeline surface preprocessing mechanisms, data acquisition systems, etc., with high automation and the ability to achieve pipeline based testing. Among them, the pipeline surface pretreatment mechanism includes a polishing mechanism and a circulating immersion system, which are used to improve the coupling effect between the pipeline wall and the ultrasonic probe. This non-destructive testing system can achieve high detection efficiency and testing accuracy, effectively solving the current problems of undersea pipeline leakage and inaccurate positioning of corrosion damage. At present, the problem of global and efficient scanning still needs to be solved, as otherwise it will be difficult to further improve work efficiency. Highlights A design of a non-destructive testing system for underwater pipelines based on ultrasound has been proposed, consisting of a three-axis control system and an ultrasonic thickness measurement system The system can realize scanning detection with high efficiency and automation The system is equipped with an automatic coupling mechanism to ensure the stability and reliability of the work

Flight test of flying wing aircraft controlled by dual synthetic jets at Ma0.2

To explore the application potential of zero-mass-flux dual synthetic jets in flight control of flying wing aircraft (FWA), dual synthetic jet actuators (DSJAs) are integrated into a FWA and flight tests without deflections of rudders are firstly carried out to verify the viability of DSJAs to manipulate three-axis attitudes at a cruising speed of 70 m/s. Two active flow control methods of circulation control and reverse jet control performed by DSJAs are utilized to execute the three-axis control. Novel flight control effectors based on DSJAs are designed and achieve the integration with the FWA. Flight tests show that three-axis flight control is realized by DSJAs distributed in different locations. The maximum roll, pitch and yaw angular velocities are 10.12°/s, 6.17°/s and 8.38°/s respectively. The work initially verifies rudderless flight control ability of DSJAs at a cruising speed of 70 m/s and the control ability will be improved by the further optimization of DSJAs.

Research on reconfiguration design of flight controller based on control allocation under actuator failure

In the condition of actuator failure, the flight control performance of the aircraft decreases. To solve this problem, considering the characteristics of multi-control surface aircraft control redundancy, a flight controller design strategy use control allocation algorithm under the condition of actuator failure is proposed. First, traditional control law module is used to generate the three-axis control commands, and then the control allocation module is designed to coordinately allocate multi-control surfaces. In the case of an actuator failure, other normal control surfaces are reallocated to reduce the impact on flight quality. The Matlab/Simulink simulation shows that when a certain actuator fails, the flight reconfiguration controller designed in this paper does not change the original control law, but only needs to reallocate the remaining normal control surfaces to ensure the desired handling quality of the aircraft.

Attitude Stabilization of a Satellite Having Only Electromagnetic Actuation Using Oscillating Controls

We consider the problem of attitude stabilization for a low Earth orbit satellite having only electromagnetic actuation. Such a satellite is not fully actuated, as the control torque is the cross-product of magnetic moment due to magnetorquers and the geomagnetic field. The aim of this work is to study whether oscillating controls can be designed such that a satellite actuated via magnetorquers alone can achieve full three-axis control irrespective of the position of the satellite. To this end, we propose considering oscillating feedback controls which generate the motion of the closed-loop system in the direction of appropriate Lie brackets. Simulation studies show that the proposed control scheme is able to stabilize the considered system.

Stability Evaluation of the SDRE Technique based on Java in a CubeSat Attitude and Orbit Control Subsystem

In 2013, the STRaND (University of Surrey and Surrey Satellite Technology Ltd) and the PhoneSat (NASA) programs attracted the attention of the aerospace community applying commercial off-the-shelf smartphones in CubeSats. Both programs deployed CubeSats using smartphones based on Google's Android, in which application development is mainly based on Java programming language. Some of these CubeSats had actuators, e.g., STRaND-1 had three reaction wheels mounted in an orthogonal configuration to provide three-axis control, whereas PhoneSat 2.0 beta had magnetorquers to de-tumble the spacecraft. Taking into account a CubeSat that runs Android operating system (based on a smartphone), it is natural to evaluate the attitude and orbit control subsystem (AOCS) based on Java. Elsewhere, we shown State-Dependent Riccati Equation (SDRE) is a feasible non-linear control technique that can be applied in such CubeSats using Java. Moreover, we shown, through simulation using a Monte Carlo perturbation model, SDRE provides better performance than the PID controller, a linear control technique. In this paper, we tackle the next fundamental problem: stability. We evaluate stability from two perspectives: (1) parametric uncertainty of the inertia tensor and (2) a Monte Carlo perturbation model based on a uniform attitude probability distribution. Through the combination of these two perspectives, we grasp the stability properties of SDRE in a broader sense. In order to handle the uncertainty appropriately, we combine SDRE with H∞. The Nanosatellite Constellation for Environmental Data Collection (CONASAT), a CubeSat from the Brazilian National Institute for Space Research (INPE), provided the nominal parameters for the simulations. The initial results of the simulations shown that the SDRE controller is stable to ± 20% uncertainty in the inertia tensor for attitudes uniformly distributed and angular velocity up to 0.15 radians/second.

A Novel Control Allocation Method for Yaw Control of Tailless Aircraft

Tailless aircraft without vertical stabilisers typically use drag effectors in the form of spoilers or split flaps to generate control moments in yaw. This paper introduces a novel control allocation method by which full three-axis control authority can be achieved by the use of conventional lift effectors only, which reduces system complexity and control deflection required to achieve a given yawing moment. The proposed method is based on synthesis of control allocation modes that generate asymmetric profile and lift induced drag whilst maintaining the lift, pitching moment and rolling moment at the trim state. The method uses low order models for aerodynamic behaviour characterisation based on thin aerofoil theory, lifting surface methodology and ESDU datasheets and is applied to trapezoidal wings of varying sweep and taper. Control allocation modes are derived using the zero-sets of surrogate models for the characterised aerodynamic behaviours. Results are presented in the form of control allocations for a range of trimmed sideslip angles up to 10 degrees optimised for either maximum aerodynamic efficiency (minimum drag for a specific yawing moment) or minimum aggregate control deflection (as a surrogate observability metric). Outcomes for the two optimisation objectives are correlated in that minimum deflection solutions are always consistent with efficient ones. A configuration with conventional drag effector is used as a reference baseline. It is shown that, through appropriate allocation of lift based control effectors, a given yawing moment can be produced with up to a factor of eight less aggregate control deflection and up to 30% less overall drag compared to use of a conventional drag effector.

Three-axis coupled flight control law design for flying wing aircraft using eigenstructure assignment method

Due to elimination of horizontal and vertical tails, flying wing aircraft has poor longitudinal and directional dynamic characteristics. In addition, flying wing aircraft uses drag rudders for yaw control, which tends to generate strong three-axis control coupling. To overcome these problems, a flight control law design method that couples the longitudinal axis with the lateral-directional axes is proposed. First, the three-axis coupled control augmentation structure is specified. In the structure, a “soft/hard” cross-connection method is developed for three-axis dynamic decoupling and longitudinal control response decoupling from the drag rudders; maneuvering turn angular rate estimation and subtraction are used in the yaw axis to improve the directional damping. Besides, feedforward control is adopted to improve the maneuverability and control decoupling performance. Then, detailed design methods for feedback and feedforward control parameters are established using eigenstructure assignment and model following technique. Finally, the proposed design method is evaluated and compared with conventional method by numeric simulations. The influences of control derivatives variation of drag rudders on the method are also analyzed. It is demonstrated that the method can effectively improve the dynamic characteristics of flying wing aircraft, especially the directional damping characteristics, and decouple the longitudinal responses from the drag rudders.

Identification Method of Geometric Deviations for Multi-Tasking Machine Tools Considering the Squareness of Translational Axes

Some methods to identify geometric deviations of five-axis machining centers have been proposed until now. However, they are not suitable for multi-tasking machine tools because of the different configuration and the mutual motion of the axes. Therefore, in this paper, an identification method for multi-tasking machine tools with a swivel tool spindle head in a horizontal position is described. Firstly, geometric deviations are illustrated and the mathematical model considering the squareness of translational axes is established according to the simultaneous three-axis control movements. The influences of mounting errors of the measuring instrument on circular trajectories are investigated and the measurements for the B axis in the Cartesian coordinate system and the measurements for the C axis in a cylindrical coordinate system are proposed. Then, based on the simulation results, formulae are derived from the eccentricities of the circular trajectories. It is found that six measurements are required to identify geometric deviations, which should be performed separately in the B axis X-direction, in B axis Y-direction, in C axis axial direction, and three times in C axis radial direction. Finally, a numerical experiment is conducted and identified results successfully match the geometric deviations. Therefore, the proposed method is proved to identify geometric deviations effectively for multi-tasking machine tools.

Influence of linear-axis error motions on simultaneous three-axis controlled motion accuracy defined in ISO 10791-6

Five-axis machine tools, which combine three linear axes and two rotary axes, are required for accuracy in machining complex shapes. In this paper, to clarify the influence of simultaneous three-axis control motion measurements as specified in ISO 10791-6, the measured results using a ball bar and R-test are compared. As the motion trajectories of the linear axes are not identical in both measurement devices, it is expected that the error motions of the linear axes cause different measurement results depending on the measurement devices. Thus, the squareness errors between the linear axes and the error motions of the linear axes are assumed as error factors that influence the measured results in this study. A mathematical model of a five-axis control machine tool that considers the error motions and squareness errors of the linear axis is constructed, and the influence of those error factors on motion accuracy is examined using an experiment and a simulation. As a result, the squareness errors and error motions of the linear axis are observed to greatly affect simultaneous three-axis controlled motion accuracy.

Dynamic analysis and stabilizing control of three-axis spherical gimbal

Nowadays, stabilized gimbals have been popular products on the present market for unmanned aerial vehicle. Rejecting multi-periodic vibration disturbance is a key point for accuracy motion of the gimbal under the flight operation of unmanned aerial vehicle. In this study, a stable control scheme of a three-axis spherical gimbal is proposed, where a new method for synthesizing multi-iterative learning control algorithm is exported. To design the controller, the mathematic modeling of the three-axis control system is earned and determined by spectrum analysis of the proposed gimbal. Performance and stability of the control system are analyzed and are evaluated in an experimental disturbance rejecting control system. Both computer simulation and experimental results are presented to illustrate the effectiveness of the proposed iterative learning controller design.

An Equivalent-Plane Cross-Coupling Position Control for Contour-Accuracy Improvement in Three-Axis Free-Form Contour Following Tasks

To reduce the contouring errors in computer-numerical-control (CNC) contour-following tasks, the cross-coupling controller (CCC) is widely researched and used. However, most existing CCCs are well-designed for two-axis contouring and can hardly be generalized to compensate three-axis curved contour following errors. This paper proposes an equivalent-plane CCC scheme so that most of the two-axis CCCs or flexibly designed algorithms can be utilized for equal control of the three-axis contouring errors. An initial-value regeneration-based Newton method is first proposed to compute the foot point from the actual motion position to the desired contour with a high accuracy, so as to establish the equivalent plane where the estimated three-dimensional contouring-error vector is included. After that, the signed contouring error is computed in the equivalent plane, thus a typical two-axis proportional-integral-differential (PID)-based CCC is utilized for its control. Finally, the two-axis control commands generated by the typical CCC are coupled to three-axis control commands according to the geometry of the established equivalent plane. Experimental tests are conducted to verify the effectiveness of the presented method. The testing results illustrate that the proposed equivalent-plane CCC performs much better than conventional method in both error estimation and error control.

Comparison Between Force-Controlled Skin Deformation Feedback and Hand-Grounded Kinesthetic Force Feedback for Sensory Substitution

Teleoperation and virtual reality systems benefit from force sensory substitution when kinesthetic force feedback devices are infeasible due to stability or workspace limitations. We compared the performance of sensory substitution when it is provided through a cutaneous method (skin deformation feedback) and a kinesthetic method (hand-grounded force feedback). For skin deformation feedback, we used a new force-controlled tactile sensory substitution device with the ability to provide tangential and normal force directly to the finger pad. Three-axis force control with 15 Hz bandwidth was achieved using a delta mechanism and three-axis force sensor. For hand-grounded force feedback, forces were grounded against the palm. As a control, world-grounded force feedback was provided using a three-degree-of-freedom kinesthetic force feedback device. Study participants were able to match a reference world-grounded force better with hand-grounded kinesthetic force feedback than with skin deformation feedback. Participants were also able to apply more accurate and precise forces with hand-grounded kinesthetic force feedback than with skin deformation feedback. Conversely, skin deformation feedback resulted in the lowest error during initial force adjustment. These experiments demonstrate relative advantages and disadvantages of skin deformation and hand-grounded kinesthetic force feedback for force sensory substitution.

Development of a precision grinding machine system for the fabrication of micro V-grooves array

The microstructures arrays are widely used and have good prospects in different applications because of their special and unique engineering functions. Micro V-grooves array is one of the most common micro structures used for optical and biomedical functions. Precision grinding is one of the micro mechanical machining technologies for a wide range of hard non-ferrous materials to fabricate micro structures array. In this paper, a three-axis computer numerical control (CNC) grinding machine tool is designed for the grinding of micro V-grooves array on hard and brittle materials. Material removal and machining strategy are studied for the grinding of V-grooves array. A machining strategy design (MSD) system is established to generate NC program, simulate the tool paths and machining process as well as predict the total machining time for the grinding of V-grooves array in the developed machine tool. Experiments are designed to grind flat surface and micro V-grooves array on optical glass. The experimental results show that the grinding machine tool can produce high quality surface and micro V-grooves array with sub-micrometer form accuracy.

Quaternion-Based Robust Satellite Attitude Tracking Control

In this paper, a
 nonlinear robust quaternion-based controller is developed to address the
 three-axis attitude tracking control problem of rigid spacecraft in presence of
 parametric uncertainties, unknown external disturbances and sensor noise. As a
 first step, a robust controller is designed that compensates parametric
 uncertainty and disturbance effects. The robust controller then reformulated to
 deal also with sensor noise. Singularity free unit quaternions are used to
 represent the attitude of the satellite in three-dimensional space. The
 Lyapunov-based stability analysis is applied to prove that a uniformly
 ultimately bounded tracking result is achieved. Simulation results are
 presented to illustrate the feasibility of the proposed control strategy. 

Dynamics and control for contactless interaction between spacecraft and tumbling debris

Tumbling debris has become a great threat to orbit activities. Contactless interaction is a novel concept for active debris removal, through which the tumbling debris no longer rotates freely but is under control. The contactless interaction method aims to de-tumble the debris and then maintain desired relative states between the spacecraft and debris. The spacecraft is simultaneously stabilized through three-axis attitude control, which makes the de-tumbling and capture operation much safer, more effective and accurate. The dynamics and control for the contactless interaction have been little studied in the past years. This paper considers a generic dynamics and control problem for contactless interaction between a spacecraft and debris. A translational and rotational dynamics model of contactless interaction is proposed and the 6-DOF equations are established. The contactless interaction control law is designed with the backstepping method, and the spacecraft three-axis control law is designed with the PD control. Simulation results show that the angular momentum is transferred from the debris to the spacecraft and the debris is thus de-tumbled. The desired relative states are achieved efficiently. Significantly, the spacecraft and debris no longer rotate in the inertial frame and, hence, the safety and accuracy for capture operation are guaranteed.

Angular Rate Sensing with GyroWheel Using Genetic Algorithm Optimized Neural Networks.

GyroWheel is an integrated device that can provide three-axis control torques and two-axis angular rate sensing for small spacecrafts. Large tilt angle of its rotor and de-tuned spin rate lead to a complex and non-linear dynamics as well as difficulties in measuring angular rates. In this paper, the problem of angular rate sensing with the GyroWheel is investigated. Firstly, a simplified rate sensing equation is introduced, and the error characteristics of the method are analyzed. According to the analysis results, a rate sensing principle based on torque balance theory is developed, and a practical way to estimate the angular rates within the whole operating range of GyroWheel is provided by using explicit genetic algorithm optimized neural networks. The angular rates can be determined by the measurable values of the GyroWheel (including tilt angles, spin rate and torque coil currents), the weights and the biases of the neural networks. Finally, the simulation results are presented to illustrate the effectiveness of the proposed angular rate sensing method with GyroWheel.

Distributed Coordination Control for Multiple Bidirectional Power Converters in a Hybrid AC/DC Microgrid

This paper proposes a distributed coordination control method for multiple bidirectional power converters (BPCs) in a hybrid ac/dc microgrid. The researched hybrid ac/dc microgrid is composed of both ac and dc subgrids connected by multiple parallel BPCs, and only the ac subgrid contains storages for the sake of economy. The proposed control method can realize the appropriate power interaction between the two subgrids and make the two subgrids to support each other, so the hybrid microgrid can operate well in both the grid-connected and islanded modes. Concretely, there are three improvements in this proposed control methods. First, a d-q-0 three-axis control strategy instead of the conventional d-q two-axis control strategy is adopted to suppress the circulating current on the ac side generated by the multiple parallel BPCs. And then the square of the dc voltage rather than the dc voltage itself is controlled, which can make the control of the dc voltage linearized and can make the BPCs provide well voltage support for the dc subgrid. Second, the dc droop control is adopted for the dc current sharing. Also, in order to relieve the storages from generating too much reactive power if the ac load reactive power is very large in the ac subgrid, the reactive power droop control is adopted to make the BPCs share some reactive power. Third, taking the capacities and load types of the two subgrids into consideration, a coordinated control strategy based on the dc voltage versus the frequency droop is designed to realize the power interaction between the two subgrids. Furthermore, the stability analysis of the proposed control method is conducted. All the conclusions are verified by the real-time hardware-in-loop tests.

Development of Four-Axis 3D Printer with Fused Deposition Modeling Technology

A new four-axis 3D printer using fused-deposition modeling (FDM) technology has been developed. The hardware components, consisting of a mechanical structure and servo-control system, and an original computer-aided machining (CAM) system were developed. Three-dimensional printers, particularly those using FDM technology, have gained popularity even in hobby use for the easy modeling of special and original parts. Three-axis control systems using stepping motors or servomotors are generally used for the development of conventional 3D printers. The nozzle portion is therefore constrained in one direction. This leads to limitations in modeling 3D shapes. Adding degrees of freedom is necessary to create more complex features. We designed a new 3D printer with multi-axis control to address this problem. Our final goal is the development of a five-axis 3D printer. We started with a four-Axis 3D printer as a first step. The number of lamination directions is increased from three to four. As conventional CAM systems cannot be used to program the desired lamination for a four-axis 3D printer, a new CAM system using the Kodatuno kernel was developed. The system can determine the nozzle orientation based on the machine tool formulation. This paper reports the developmental background and an overview of the developed machine tool as well as its characteristics, its evaluation results, and our future plans.