Gimbal Mechanism Research Articles

Integrated attitude—orbit control of solar sail with single-axis gimbal mechanism

A new attitude control method for solar sails is proposed using a single-axis gimbal mechanism and three-axis reaction wheels. The gimbal angle is varied to change the geometrical relationship between the force due to solar radiation pressure (SRP) and the center of mass of the spacecraft, such that the disturbance torque is minimized during attitude maintenance for orbit control. Attitude maneuver and maintenance are performed by the reaction wheels based on the quaternion feedback control method. Even if angular momentum accumulates on the reaction wheels due to modelling error, it can also be unloaded by using the gimbal to produce suitable torque due to SRP. In this study, we analyzed the attitude motion under the reaction wheel control by linearizing the equations of motion around the equilibrium point. Further, we newly derived the propellent-free unloading method based on the analytical formulation. Finally, we constructed the integrated attitude-orbit control method, and its validity was verified in integrated attitude-orbit control simulations.

A Study on Robust Finite-Time Visual Servoing with a Gyro-Stabilized Surveillance System

This article presents the design and validation of a novel visual servoing scheme for a surveillance system. In this system, a two-axis gimbal mechanism operates the rotation of a camera which is able to provide visual information on the tracked target for the control system. The control objective is to bring the target’s projection to the center of the image plane with the smallest steady-state error and a smooth transient response, even with the unpredictable motion of the target and the influence of external disturbances. To fulfill these tasks, the proposed control scheme is designed consisting of two parts: (1) an observer estimates simultaneously the matched and unmatched disturbances; and (2) a motion control law guarantees the finite-time stability and visual servoing performance. Finally, experiments are conducted for validation and evaluation. The proposed control system shows its consistency and ought to perform better than previous approaches.

Active Object Detection and Tracking Using Gimbal Mechanisms for Autonomous Drone Applications

Object recognition, localization, and tracking play a role of primordial importance in computer vision applications. However, it is still an extremely difficult task, particularly in scenarios where objects are attended to using fast-moving UAVs that need to robustly operate in real time. Typically the performance of these vision-based systems is affected by motion blur and geometric distortions, to name but two issues. Gimbal systems are thus essential to compensate for motion blur and ensure visual streams are stable. In this work, we investigate the advantages of active tracking approaches using a three-degrees-of-freedom (DoF) gimbal system mounted on UAVs. A method that utilizes joint movement and visual information for actively tracking spherical and planar objects in real time is proposed. Tracking methodologies are tested and evaluated in two different realistic Gazebo simulation environments: the first on 3D positional tracking (sphere) and the second on tracking of 6D poses (planar fiducial markers). We show that active object tracking is advantageous for UAV applications, first, by reducing motion blur, caused by fast camera motion and vibrations, and, second, by fixating the object of interest within the center of the field of view and thus reducing re-projection errors due to peripheral distortion. The results demonstrate significant object pose estimation accuracy improvements of active approaches when compared with traditional passive ones. More specifically, a set of experiments suggests that active gimbal tracking can increase the spatial estimation accuracy of known-size moving objects, under conditions of challenging motion patterns and in the presence of image distortion.

A Fast Self-Calibration Method for Dual-Axis Rotational Inertial Navigation Systems Based on Invariant Errors.

In order to ensure that dual-axis rotational inertial navigation systems (RINSs) maintain a high level of accuracy over the long term, there is a demand for periodic calibration during their service life. Traditional calibration methods for inertial measurement units (IMUs) involve removing the IMU from the equipment, which is a laborious and time-consuming process. Reinstalling the IMU after calibration may introduce new installation errors. This paper focuses on dual-axis rotational inertial navigation systems and presents a system-level self-calibration method based on invariant errors, enabling high-precision automated calibration without the need for equipment disassembly. First, navigation parameter errors in the inertial frame are expressed as invariant errors. This allows the corresponding error models to estimate initial attitude even more rapidly and accurately in cases of extreme misalignment, eliminating the need for coarse alignment. Next, by utilizing the output of a gimbal mechanism, angular velocity constraint equations are established, and the backtracking navigation is introduced to reuse sensor data, thereby reducing the calibration time. Finally, a rotation scheme for the IMU is designed to ensure that all errors are observable. The observability of the system is analyzed based on a piecewise constant system method and singular value decomposition (SVD) observability analysis. The simulation and experimental results demonstrate that this method can effectively estimate IMU errors and installation errors related to the rotation axis within 12 min, and the estimated error is less than 4%. After using this method to compensate for the calibration error, the velocity and position accuracies of a RINS are significantly improved.

Effect of Coulomb Friction on Feedback Posture Control of Bicycle Using Gyroscopic Moment Effect

A mechanism has been proposed that utilizes the gyroscopic moment generated by tilting the rotation axis of a flywheel for stabilization control of unstable system. In this study, we investigate the effectiveness of feedback control which drives a gimbal mechanism to maintain the standing posture of an unstable structure such as a two-wheel vehicle. Although a simple feedback of posture angle enables a two-wheel structure to keep standing, both posture and gimbal continue shaking little by little. This is because the gimbal temporarily stays at a constant angle due to the action of Coulomb friction, and the system becomes unstable in the interim. We propose a method to estimate both the length of time when the motion of the gimbal stops and the amplitudes of the vibration of posture and gimbal. Here, we assume that the first-order mode poles obtained from the linearized model are complex numbers and that the second-order mode response converges immediately. From the experimental results, it is found that if the gimbal stays at a constant angle for a long time, the structure tends to fall over. We show that state feedback is necessary to realize to shorten the time when the gimbal stays at a constant angle and to reduce the amplitudes of oscillations at the same time.

Autonomous Wheel Off-Loading Strategies for Deep-Space CubeSats

Deep-space CubeSats missions require careful trade-offs on design drivers such as mass, volume, and cost, while ensuring autonomous operations. This work elaborates the possibility of off-loading the reaction wheels without the need of carrying a bulky and expensive reaction control system or the field-dependent magnetotorquers. The momentum accumulated along two body axes can be removed by either offsetting the main thruster with a gimbal mechanism or by tilting differentially the solar wings. The dumping on the third axis can be still accomplished by imposing a specific attitude trajectory with the motion of either the gimbal or the arrays drive mechanism. The M-Argo CubeSat is selected as case study to test the techniques along its deep-space trajectory. The strategies decision-making is autonomously carried out by a state machine. The off-loading during the cruising arcs employs the gimballed thruster and takes typically 3 h, granting a mass savings of more than 99% with respect to the usage of a reaction control system. The trajectory is shown to have negligible differences with respect to the nominal one, since the thrust is corrected accordingly. During the coasting arcs, the solar arrays are tilted and several hours are required, depending on the Sun direction and intensity, but the propellant is completely saved. Sensitivity analyses are also carried out on the initial angular momentum components and the center of mass displacement to check the robustness of the algorithms.

Orientation Modeling Using Quaternions and Rational Trigonometry

In recent years, the recreational and commercial use of flight and driving simulators has become more popular. All these applications require the calculation of orientation in either two or three dimensions. Besides the Euler angles notation, other alternatives to represent rigid body rotations include axis-angle notation, homogeneous transformation matrices, and quaternions. All these methods involve transcendental functions in their calculations, which represents a disadvantage when these algorithms are implemented in hardware. The use of transcendental functions in software-based algorithms may not represent a significant disadvantage, but in hardware-based algorithms, the potential of rational models stands out. Generally, to calculate transcendental functions in hardware, it is necessary to utilize algorithms based on the CORDIC algorithm, which requires a significant amount of hardware resources (parallel) or the design of a more complex control unit (pipelined). This research presents a new procedure for model orientation using rational trigonometry and quaternion notation, avoiding trigonometric functions for calculations. We describe the orientation of a gimbal mechanism presented in many applications, from autonomous vehicles such as cars or drones to industrial manipulators. This research aims to compare the efficiency of a rational implementation to classical modeling using the techniques mentioned above. Furthermore, we simulate the models with software tools and propose a hardware architecture to implement our algorithms.

LookOut! Interactive Camera Gimbal Controller for Filming Long Takes

The job of a camera operator is challenging, and potentially dangerous, when filming long moving camera shots. Broadly, the operator must keep the actors in frame while safely navigating around obstacles and while fulfilling an artistic vision. We propose a unified hardware and software system that distributes some of the camera operator’s burden, freeing the operator up to focus on safety and aesthetics during a take. Our real-time system provides solo operators with end-to-end control so that they can balance on-set responsiveness to action against planned storyboards and framing while looking where they are going. By default, we film without a field monitor. Our LookOut system is built around a lightweight commodity camera gimbal mechanism, with heavy modifications to the controller, which would normally just provide active stabilization. Our control algorithm reacts to speech commands, video, and a premade script. Specifically, our automatic monitoring of the live video feed saves the operator from distractions. In preproduction, an artist uses our graphical user interface (GUI) to design a sequence of high-level camera “behaviors.” Those can be specific, based on a storyboard, or looser objectives, such as “frame both actors.” Then, during filming, a machine-readable script, exported from the GUI, ties together with the sensor readings to drive the gimbal. To validate our algorithm, we compared tracking strategies, interfaces, and hardware protocols and collected impressions from (a) filmmakers who used all aspects of our system and (b) filmmakers who watched footage filmed using LookOut.

Design and control of 2-DoF joystick using MR-fluid rotary actuator

The purpose of this paper is to design a control algorithm for a 2-DoF rotary joystick model. Firstly, the structure of the joystick, which composes of two magneto-rheological fluid actuators (shorten MRFA) with optimal configuration coupled perpendicularly by the gimbal mechanism to generate the friction torque for each independent rotary movement, is introduced. The control strategy of the designed joystick is then suggested. Really, because of two independent rotary movements, it is necessary to design two corresponding controllers. Due to hysteresis and nonlinear dynamic characteristics of the MRFA, controllers based an accurate dynamic model are difficult to realize. Hence, to release this issue, the proposed controller (named self-turning fuzzy controllers-STFC) will be built through the fuzzy logic algorithm in which the parameters of controllers are learned and trained online by Levenberg-Marquardt training algorithm. Finally, an experimental apparatus will be constructed to assess the effectiveness of the force feedback controls. Herein, three experimental cases are performed to compare the control performance of open-loop and close-loop control method, where the former is done through relationship between the force at the knob and the current supplied to coil while the latter is realized based on the proposed controller and PID controller. The experimental results provide strongly the ability of the proposed controller, meaning that the STFC is robust and tracks well the desirable force with high accuracy compared with both the PID controller and the open-loop control method.

Control of an Omnidirectional UAV for Transportation and Manipulation Tasks

This paper presents a motion control scheme for a new concept of omnidirectional aerial vehicle for transportation and manipulation tasks. The considered aerial platform is a novel quadrotor with the capability of providing multi-directional thrust by adding an actuated gimbal mechanism in charge of modifying the orientation of the frame on which the four rotors are mounted. The above mechanical design, differently from other omnidirectional unmanned aerial vehicles (UAVs) with tilted propellers, avoids internal forces and energy dissipation due to non-parallel propellers’ axes. The proposed motion controller is based on a hierarchical two-loop scheme. The external loop computes the force to be applied to the vehicle and the reference values for the additional joints, while the inner loop computes the joint torques and the moment to be applied to the multirotor. In order to make the system robust with respect to the external loads, a compensation of contact forces is introduced by exploiting the estimate provided by a momentum based observer. The stability of the motion control scheme is proven via Lyapunov arguments. Finally, two simulation case studies prove the capability of the omnidirectional UAV platform to track a 6-DoFs trajectory both in free motion and during a task involving grasping and transportation of an unknown object.

An Over-Actuated Multi-Rotor Aerial Vehicle With Unconstrained Attitude Angles and High Thrust Efficiencies

Fully-actuated multi-rotor aerial platforms are receiving increasing research interests for the capability of six degree-of-freedom (DOF) motions such as hovering at non-horizontal attitude angles. Existing real world hardware and experiments have demonstrated such capability for a limited range of angles. This letter presents an aerial platform that achieves maneuvering at arbitrary attitudes with uniformly high thrust efficiencies. We propose a novel vectoring thrust force actuator by mounting a regular quadcopter on a passive mechanical gimbal mechanism. The UAV platform achieves full six-DOF motion with redundancies from four of these vectoring thrust actuators. We present the hierarchical controller, which generates high-level virtual wrench commands, allocations to actuators, and low-level actuator controls. We demonstrate the first real-world experiments of any pose maneuver over 360 degrees without requiring unwrapping rotations.

Absolute multilateration-based coordinate measurement system using retroreflecting glass spheres

We have measured the three-dimensional coordinates of retroreflecting glass spheres using a multilateration technique. To this end, the distances between each target and our measurement heads have been determined by an in-house prototype of electro-optical absolute distance meter. The used targets are spheres of glass refractive index n = 2 and of diameter 14.2 mm. They offer a much larger aperture than corner cubes and a lower cost, but they present a low reflectivity. However, this paper shows that with a proper collimation of the laser beams it is possible to reach a range of operation of 20 m. The standard uncertainty on such distances is better than 11 μm, including the mechanical errors of the gimbal mechanisms of our aiming systems. This uncertainty has been validated thanks to a comparison with an interferometric bench. In addition, the measurement of the coordinates of 16 glass spheres using a self-calibration multilateration algorithm has also confirmed the performances of the developed system: the standard deviation on the position errors has been estimated to about 10 μm.

OBJECT TRACKING CONTROL USING A GIMBAL MECHANISM

Abstract. This work describes a control solution for real time object tracking in images acquired for a RPAS on an object inspection environment. This, controlling a 3-axis gimbal mechanism to control a camera orientation embedded to a RPAS, using its image processed for feedback. The objective of control is to maintain the target of interest at the center of the image plane. The proposed solution uses a YOLOv3 object detection model in order to detect the target object and determine, thru rotation matrices, the new desired angles to converge the object’s position to the center of the image. To compare results of the proposed control, a linear control was tuned using a linear PI algorithm. Simulation and practice experiments successfully tracked the desired object in real time using YOLOv3 in both control approaches presented.

Проектування та виготовлення пристрою юстирування на основі карданного механізму

З метою закріплення позитивної лінзи на рейтері оптичної лави та можливості її юстирування навколо двох осей було запропоновано спроектувати та виготовити юстирувальний вузол у принцип конструкції якого покладено так званий карданний механізм.
 У результаті розроблення та конструювання отримано кресленики вузла юстирування із застосуванням карданного механізму та окремих його деталей. Під час проведення проектних робіт було враховано, що деталі вузла друкуватимуться із застосуванням 3D-друку.
 під час проведення даної проектно-конструкторської роботи було спроектовано та виготовлено вузол юстирування позитивної лінзи із застосуванням карданного механізму, який здатний виконувати покладені на нього функції та може застосовуватись для демонстрації можливостей адитивних технологій, цікавих за конструкцією оптичних вузлів та показувати студентам доцільність та необхідність набуття нових знань та умінь за обраною спеціальністю та освітньою програмою.
 
 In order to fix the positive lens on the reiter of the optical bench and the possibility of its adjustment around the two axes, it was proposed to design and manufacture an adjustment unit in the principle of construction of which is the so-called cardan mechanism. As a result of development and design, drawings of the adjustment unit with the use of the cardan mechanism and its individual parts were obtained. During the design work, it was taken into account that the details of the node will be printed using 3D printing. During this design work, a positive lens adjustment unit was designed and manufactured using a gimbal mechanism that is able to perform its functions and can be used to demonstrate the capabilities of additive technologies of interest in the design of optical units and show students the feasibility and necessity of acquiring new ones. knowledge and skills in the chosen specialty and educational program.

Empirical Modeling of 2-Degree-of-Freedom Azimuth Underwater Thruster Using a Signal Compression Method

This paper presents an empirical modeling of a 2-Degree-of-Freedom (DoF) azimuth thruster using the signal compression method. The thruster has a gimbal mechanism with two servo motors and generates thrust in arbitrary directions. This mechanism can reduce the number of thrusters in an underwater robot and contribute to compact design. When an underwater robot is controlled with azimuth thrusters, the influence from the rotational motion of the thruster has to be considered, and a dynamic model of the azimuth thruster is needed. It is difficult to derive an analytical model because the system model depends on complicated fluid dynamics. In this study, empirical models of force and moment for rotational motion were derived for practical use through frequency analysis. A signal compression method can effectively extract the system model in the frequency domain from just the mechanically constrained frequency response. Experiments were carried out using a force/torque sensor that was connected to a cantilever in a water tank. The system model was analyzed with Bode plots, and the model coefficients were derived through curve fitting. The derived model was verified by a validation experiment.

Redesigning dispenser component to enhance performance crop-dusting agriculture drones

Abstract Agricultural drones are Unmanned Aerial Vehicles (UAVs) applied to farming in order to help increase crop production and improve farm efficiency. Crop-dusting drones are able to spray powdered fertilizer, pesticide, or insecticide on crops from the air, resulting in reduced costs and increased efficiency compared to traditional methods. The objective of this research work was to improve and enhance the performance of the crop-dusting process using agricultural drones. This research paper details the development of an improved storage container design and stabilized release mechanism for crop-dusting. To stabilise the release of payload when the drone is moving or swaying in the air, a gimbal mechanism was added to the release mechanism in which weights were used to produce constant downward force which balances the mechanism. Tests conducted on the prototype system showed that it performs as required. The stabilization tests show an improvement in accuracy of granule spread when using the stabilized release mechanism developed in this research work. As such, the wastage of fertilizers and pesticides can be reduced. The prototype system was also found to much more capable at carrying heavier loads for a longer period of time compared to current designs. Thus, using the prototype system developed for this research work, the size of storage container as well as the weight of fertilizer or pesticide granule payloads can be increased.

Structural design of a microsurgery-specific haptic device: neuroArmPLUSHD prototype

A microsurgery-specific haptic interface with articulated structure, possessing 3 active, 4 passive and 3 supplementary degrees of freedom (DOFs), was designed and developed. The system includes a 3-DOF active serial linkage design, mimicking the human upper extremity. It is combined with a microsurgery-specific end-effector, comprised of a 3-DOF passive gimbal mechanism and a 1-DOF passive exchangeable surgical toolset. The spherical gimbal workspace twinned with the larger linkage arm workspace allow accurate and delicate movements to maneuver the surgical tool in narrow corridors, corresponding to conventional surgery. The structural design of the device is based on kinematic performance measures aimed to enhance ergonomics and mitigate training limitations of novice end-users. A supplementary 3-DOF adjustable base further improved ergonomics for end-users of different sizes. Force feedback was provided to improve safety, i.e. avoidance of force errors in execution of surgical tasks. This haptic interface provides high positional and output force resolution (0.92–1.46 mm in Cartesian coordinate system and 0.2 N, respectively), wide range of allowable force (up to 15 N), high global manipulability (0.77), global isotropy (0.68) and stiffness (2.3 N/mm). The work, indeed, introduces a novel kinematic performance index, Dexterous Conditioning Index (DCI), based on the volume of dexterous workspace, correlating to ease of use and decreased singularity. Accordingly, the proposed haptic device demonstrates a high level of accuracy, haptic feedback, dexterous workspace, and performance, ideal for implementation in robot-assisted microsurgery.

Design of Robust Fault-Tolerant Control for Target Tracking System With Input Delay and Sensor Fault

This paper presents a robust fault-tolerant control scheme that provides reliable tracking and effective disturbance rejection for a low-cost tracking system. As the controlled apparatus, a 2-axis gimbaled mechanism is involved in a networked control system, and an unreliable sensor brings sensor drift into the system. Besides, external disturbances heavily affect the system in practical applications. Representation of the faulty gimbal system with its constraints and disturbances is firstly introduced. Then, the design of the fault-tolerant controller is detailed, which consists of two components: (1) an unknown input observer that estimates the fault and effect of disturbances and network delay simultaneously, and (2) a robust control law, using the observer estimations, designed based on the combination of the super-twisting algorithm, backstepping procedure, and integral sliding mode control technique. Subsequently, simulations and experiments are conducted, in which the performance of the proposed control system is compared to those from the previous studies. The results show the superiority and reliability of the proposed control system.

Autonomous Mobile Robot for Outdoor Slope Using 2D LiDAR with Uniaxial Gimbal Mechanism

The Nakanoshima Challenge is a contest for developing sophisticated navigation systems of robots for collecting garbage in outdoor public spaces. In this study, a robot named Navit(oo)n is designed, and its performance in public spaces such as city parks is evaluated. Navit(oo)n contains two 2D LiDAR scanners with uniaxial gimbal mechanism, improving self-localization robustness on a slope. The gimbal mechanism adjusts the angle of the LiDAR scanner, preventing erroneous ground detection. We evaluate the navigation performance of Navit(oo)n in the Nakanoshima and its Extra Challenges.

Geometric and constrained control for a string of tethered drones

In this study, we present a novel concept of a multi tethered drone system. The system includes an arbitrary number of drones connected serially to an active ground station. The considered drones are of quadrotor type. Utilizing a unique pulley–gimbal mechanism, each drone can freely move along the tether, and its state is measured with respect to the ground station without the use of standard onboard inertial sensors or GPS. The proposed system can be thought of as a robotic arm where each tether section acts as a variable-length link and each drone is a joint actuator. We model the coupled behavior of the ground station and the string, taking into account an arbitrary number of drones. Then, a controller that combines tools from geometric-control and Model Predictive Control is suggested. The developed model and control approach are also applicable for other swarm applications where the position of agents is to be controlled to a string-like form. Finally, the concept is demonstrated using numerical simulations and an initial experiment, which illustrate its potential effectiveness.