Position Control Of Manipulator Research Articles

Modeling and Control of a Hybrid Multi DOF Motor for a Tilted Rotating System

This paper presents the design, modeling, and control of a hybrid multi-degree-of-freedom motor (HMDOF motor) that can be applied to unmanned aerial vehicles, such as drones. The HMDOF motor has a rotating motor and tilting motors separately and enables multi-DOF movement by driving each motor. In addition, owing to its structural characteristics, it is designed to allow a 3- or 6-DOF movement in only one motor. In this study, the control performance of an HMDOF motor was verified using simulated and experimental results. The position control performance for the rotation speed of the rotating motor was verified, and the control performance of the motor under the speed of the rotating motor and disturbance on tilting motors were analyzed.

Modeling and Experimental Evaluation of a Pneumatic Variable Stiffness Actuator

The variable stiffness actuator (VSA) can absorb and reuse positive–negative power between the load and the motor, which can enhance the actuating efficiency of robotic joints and improve their impact resistance. Typical VSAs mainly adopted a motor-mechanism system into the elastomer in addition to the main actuating motor to adjust elastomer stiffness, which might limit practical effects due to large mass and inertial of the variable stiffness elastomer. This article proposes a new type of a pneumatic variable stiffness actuator (PVSA), which uses a rotating cylinder and compressed gas to form a lightweight pneumatic elastomer, the stiffness of which could be adjusted via a remote pressure controlling system, thus improving the mass distribution of the VSA in lightweight space-constrained actuation. In addition, the PVSA could also be integrated with metal springs to increase its stiffness range and torque bandwidth, further improving its practical application prospect. The influence of the friction, the backlash, and the temperature on PVSA performance are theoretically and experimentally analyzed, and its position, torque, and stiffness control performance under variable situations are tested and verified through multiple simulations and experiments. The results indicate that the PVSA can provide expected actuation performance with effective remote stiffness adjustment capability.

A Sensorless Control Strategy for Permanent Magnet Synchronous Motor at Low Switching Frequency

The high-frequency (HF) square-wave voltage injection method can be used in permanent magnet synchronous motor (PMSM) drive systems. However, when the switching frequency is too low, the injection frequency will also decrease, which will reduce the update frequency of the HF response current, making it difficult to extract the position quadrature signal and affecting the accuracy of position estimation and control performance. This paper proposes a method for extracting position quadrature signals based on sampling rate transformation, and a signal processing strategy based on Cascade Integrator Comb (CIC) interpolation filtering, which can solve the problem of waveform distortion caused by the low sampling rate of the extracted position quadrature signal. This strategy can increase the sampling rate of the position quadrature signal to the pulse width modulation (PWM) update frequency by interpolating in the sampling current, thereby reducing the harmonic content of the position quadrature signal and improving the position estimation. precision. In addition, the PWM update frequency and estimated rotational speed information are used to compensate for the delay caused by position estimation and inverter update, which effectively improves the accuracy of position estimation. Finally, the effectiveness of the proposed control strategy is verified by simulation.

Research on PID Position Control of a Hydraulic Servo System Based on Kalman Genetic Optimization

With the wide application of hydraulic servo technology in control systems, the requirement of hydraulic servo position control performance is greater and greater. In order to solve the problems of slow response, poor precision, and weak anti-interference ability in hydraulic servo position controls, a Kalman genetic optimization PID controller is designed. Firstly, aiming at the nonlinear problems such as internal leakage and oil compressibility in the hydraulic servo system, the mathematical model of the hydraulic servo system is established. By analyzing the working characteristics of the servo valve and hydraulic cylinder in the hydraulic servo system, the parameters in the mathematical model are determined. Secondly, a genetic algorithm is used to search the optimal proportional integral differential (PID) controller gain of the hydraulic servo system to realize the accurate control of valve-controlled hydraulic cylinder displacement in the hydraulic servo system. Under the positioning benchmark of step signal and sine wave signal, the PID algorithm and the genetic optimized PID algorithm are compared in the system simulation model established by Simulink. Finally, to solve the amplitude fluctuations caused by the GA optimized PID and reduce the influence of external disturbances, a Kalman filtering algorithm is added to the hydraulic servo system to reduce the amplitude fluctuations and the influence of external disturbances on the system. The simulation results show that the designed Kalman genetic optimization PID controller can be better applied to the position control of the hydraulic servo system. Compared with the traditional PID control algorithm, the PID algorithm optimized by genetic algorithm improves the system’s response speed and control accuracy; the Kalman filter is a good solution for the amplitude fluctuations caused by GA-optimized PID that reduces the influence of external disturbances on the hydraulic servo system.

Vibration attenuation of a propulsion shafting system by electromagnetic forces: Static thrust force balance and harmonic vibration suppression

Suppressing the vibration of the thrust bearing and its transmission in a shafting system induced by the thrust force is an important measure to reduce low-frequency vibration and sound radiation. However, it is difficult to attenuate low-frequency vibration transmission from the shaft to the hull under the high-speed and heavy-load condition. An active control scenario is proposed to suppress the longitudinal vibration of the thrust bearing and its pedestal, in which an electromagnetic constraint is applied to balance the static thrust force while two inertial electromagnetic actuators are used to suppress the harmonic vibration of the bearing pedestal. The dynamic model of a shaft-foundation system with electromagnetic control forces is established on the basis of the modified Ritz method. A longitudinal position control method to balance the thrust force is built and the performance of position control and vibration attenuation is evaluated. The feasibility of the longitudinal vibration control of the bearing pedestal is analyzed, and the effectiveness of the proposed scenario for longitudinal vibration transmission attenuation is evaluated by combining the longitudinal position control of the shaft with the harmonic vibration suppression of the bearing pedestal. Simulations and experiments demonstrate that the proposed active control scenario is effective in longitudinal position adjustment and vibration attenuation.

Fault diagnosis and accommodation for multi-actuator faults of a fixed-wing unmanned aerial vehicle

This study proposes a system design scheme of fault detection, isolation, and accommodation algorithms for the actuator fault of a fixed-wing unmanned aerial vehicle (FW-UAV) by considering system nonlinearity, external disturbance, and multi-actuator faults. The fault diagnosis scheme consists of a comprehensive observer and a bank of fault isolation estimators designed based on the actuator of the FW-UAV. In the diagnosis module, the system model is transformed into two systems by introducing a transformation matrix, so that both the actuator faults and the system disturbance are separated. Then, the concept of equivalent output injection is applied to construct a comprehensive observer to detect the actuator fault and estimate the unknown system disturbance. In the isolation estimation module, a set of sliding mode observers (SMOs) is constructed to isolate the multi-actuator faults, which reveals the fault source precisely. The stability analysis of the proposed SMOs was derived from the solution of linear matrix inequalities. In the event of a fault, the fault estimation provided by the fault diagnosis solution is used to accommodate the fault effects, while maintaining good attitude control and position tracking performance of the FW-UAV. The effectiveness of the proposed scheme is verified by the simulation model of de Havilland DHC-2 ‘Beaver’ aircraft in different fault cases.

A Reconfigurable Leg for Walking Robots

We present the design of a robotic leg that can seamlessly switch between a spring-suspended-, and unsuspended configuration. Switching is realized by a mechanism that exploits the alternative configuration of the two-link leg. The mechanism is lightweight, does not require additional actuation, and only relies on the leg movement for engagement. We validated the performance of the prototype leg on a single-leg testbed and investigated the power consumption during standing, crouching, and hopping in both configurations. The experiments showed that the efficiency of hopping and cyclic base height control is better with the spring-suspended configuration. However, it can undermine the leg's performance in position control and requires higher torque to maintain low base height, where the unsuspended configuration has advantages. Overall, the switching ability allows for seamlessly selecting the optimal mode for a specific locomotion task.

Output feedback model predictive control of spacecrafts based on proportional-integral observer

A novel attitude control algorithm is developed for spacecrafts based on the model predictive control and proportional-integral observer (PIO) in the presence of constraints. The high dimensional nonlinear dynamics are firstly transformed into three single-input single-output linear structural subsystems with coupled actions. Then these actions are viewed as disturbances estimated by the PIOs, and their values are embedded into the models to improve the accuracy of prediction. The predictive controller is composed of the analytical solution and the heuristic constraint handling. In addition, the angular position information is only needed for implementation. Finally, several simulations are used to verify the effectiveness of the developed algorithm. The results show that the designed system compensates the coupled actions well and makes the attitude control performance good.

Position Control of Quadrotor UAV Based on Cascade Fuzzy Neural Network

In this article, a cascade fuzzy neural network (FNN) control approach is proposed for position control of quadrotor unmanned aerial vehicle (UAV) system with high coupling and underactuated. For the attitude loop with limited range, the FNN controller parameters were trained offline using flight data, whereas for the position loop, the method based on FNN compensation proportional-integral-derivative (PID) was adopted to tune the system online adaptively. This method not only combined the advantages of fuzzy systems and neural networks but also reduced the amount of calculation for cascade neural network control. Simulations of fixed set point flight and spiral and square trajectory tracking flight were then conducted. The comparison of the results showed that our method had advantages in terms of minimizing overshoot and settling time. Finally, flight experiments were carried out on a DJI Tello quadrotor UAV. The experimental results showed that the proposed controller had good performance in position control.

Adaptive Attitude Control of a Quadrotor Using Fast Nonsingular Terminal Sliding Mode

As one type of unmanned aerial vehicles, the quadrotor typically suffers from payload variations, system uncertainties, and environmental wind disturbances, which significantly deteriorate its attitude control performance. To provide high-speed, accurate, and robust attitude tracking performance for the quadrotor, an adaptive fast nonsingular terminal sliding mode (AFNTSM) controller is proposed in this article. The proposed AFNTSM controller combines the advantages of fast nonsingular terminal sliding mode (FNTSM), integral sliding mode, and adaptive estimation techniques, which are effective to achieve the desired tracking performance and suppress control signal chattering. Furthermore, unlike conventional methods, the adaptive estimation removes the requirements for the upper bound information of the disturbances. It is proved that the proposed AFNTSM can guarantee finite-time convergence and zero tracking error for the quadrotor attitude control. Finally, comparative study with the FNTSM control only and conventional sliding mode control is conducted through experiments and the results demonstrate that the proposed AFNTSM can achieve faster convergence and stronger robustness in line with theoretical analysis.

Motion and Force Control of Servo Die Cushion System using Bilateral Control

Servo die cushion systems perform position control for pre-acceleration function to reduce the impact force between slider and cushion, and force control of the blank holder to avoid fracture and wrinkling. This paper applies bilateral control to perform position and force control with a hybrid switching strategy for smoothly switching between the pre-acceleration and blank holder force control. Implementation on a test rig verifies the proposed method.

Dynamic Behavior Analysis and Stability Control of Tethered Satellite Formation Deployment.

In recent years, Tethered Space Systems (TSSs) have received significant attention in aerospace research as a result of their significant advantages: dexterousness, long life cycles and fuel-less engines. However, configurational conversion processes of tethered satellite formation systems in a complex space environment are essentially unstable. Due to their structural peculiarities and the special environment in outer space, TSS vibrations are easily produced. These types of vibrations are extremely harmful to spacecraft. Hence, the nonlinear dynamic behavior of systems based on a simplified rigid-rod tether model is analyzed in this paper. Two stability control laws for tether release rate and tether tension are proposed in order to control tether length variation. In addition, periodic stability of time-varying control systems after deployment is analyzed by using Floquet theory, and small parameter domains of systems in asymptotically stable states are obtained. Numerical simulations show that proposed tether tension controls can suppress in-plane and out-of-plane librations of rigid tethered satellites, while spacecraft and tether stability control goals can be achieved. Most importantly, this paper provides tether release rate and tether tension control laws for suppressing wide-ranging TSS vibrations that are valuable for improving TSS attitude control accuracy and performance, specifically for TSSs that are operating in low-eccentricity orbits.

Design of Position Control Method for Pump-Controlled Hydraulic Presses via Adaptive Integral Robust Control

This paper takes the position control performance of pump-controlled hydraulic presses as the research object. The control methods are designed respectively for the two motion stages of rapid descent and slow descent of hydraulic presses in order to improve the control performance of the system. First of all, the accuracy model of the pump-controlled hydraulic presses position servo system (the pump-controlled hydraulic presses position servo system, which is called PCHPS) and its MATLAB/Simulink simulation platform are established. Based on the theoretical analysis and experimental data, the interference factors affecting the tracking accuracy and positioning accuracy of the PCHPS are analyzed. Then, an adaptive integral robust control (the adaptive integral robust control, which is called AIRC) for PCHPS is designed to reduce the influence of nonlinear factors on the system, and the effectiveness of the controller is verified by simulation. Finally, the position control experiment of PCHPS is designed, and the experimental results show that the AIRC can effectively reduce nonlinear factors such as unknown interference in the slow-down stage of the system. The positioning accuracy is raised to within 0.008 mm, which improves the process level of the hydraulic presses.

Trajectory tracking of tail-sitter aircraft by ℓ1 adaptive fault tolerant control

This paper proposes an &#x2113;<inf>1</inf> adaptive fault tolerant control method for trajectory tracking of tail-sitter aircraft in the state of motor loss fault. The tail-sitter model considers the uncertainties produced by the features of nonlinearities and couplings which cause difficulties in control. An &#x2113;<inf>1</inf> adaptive controller is designed to reduce the position and attitude error when actuators have faults. A reference trajectory containing large maneuver flight transitions is designed, which makes it even harder for the &#x2113;<inf>1</inf> controller to track accurately. Compensators are designed to assist &#x2113;<inf>1</inf> adaptive controller tracking of the reference trajectory. The stability of the &#x2113;<inf>1</inf> adaptive controller including compensators is proved. Finally, the simulation results are used to analyse the effectiveness of the proposed controller. Compared to the H<inf>&#x221E;</inf> controller, the &#x2113;<inf>1</inf> adaptive controller with compensators has better performance in position control and attitude control under fault tolerance state even when the aircraft conducts large maneuver. Besides, as the &#x2113;<inf>1</inf> adaptive control method separates feedback control and adaptive law design, the response speed of the whole system is improved.

ARX, ARMAX, Box-Jenkins, Output-Error, and Hammerstein Models for Modeling Intelligent Pneumatic Actuator (IPA) System

A pneumatic actuator is highly nonlinear, which makes the precise position control of this actuator difficult to achieve. In order to achieve precise control, selecting a suitable model structure is a prerequisite before control estimation. This selection of the model structure is based upon an understanding of the physical systems. In this paper, the black-box model is chosen as a system identification model for modeling position control of an Intelligent Pneumatic Actuator (IPA) system and a variety of parametric model structures. The parametric model structure, such as ARX, ARMAX, Box-Jenkins, output-error structures, and Hammerstein available in the black-box model, is used to assist in modeling the IPA system. The results indicate that Hammerstein had the best performance for modeling position control of the IPA system with the best fit 94.95. Also, the results show that ARX, ARMAX, Box-Jenkins, and output-error structures had best fit more than 90%.

Intelligent Permanent Magnet Motor-Based Servo Drive System Used for Automated Tuning of Piano

This paper presents an intelligent permanent magnet synchronous motor-based servo drive system used in automated piano tuning applications. The permanent magnet synchronous motor-based drives are able to improve the accuracy of the piano tuning process in comparison with the traditional direct-current motor-based and step motor-based servo drives. To explain the techniques, firstly, the structure and principles of the automated piano tuning devices with a surface-mounted permanent magnet synchronous motor-based drive system integrated are introduced, illustrating that it is feasible to implement the proposed piano tuning strategy. Secondly, the piano tuning devices have two functions: low-speed rotation and position holding. To ensure that the surface-mounted permanent magnet synchronous motor can rotate stably over the low-speed range with strong anti-interference capacity, a double closed-loop speed-regulation-based control scheme is employed. And to ensure high position control performance, a fuzzy-adaptive triple closed-loop position-regulation-based control scheme is employed. It terms of the control schemes, it deserves to be mentioned that main contributions include, firstly, the parameters of the proportional integral controllers in the double closed-loop speed-regulation structure is tuned relying on both stability and bandwidth analyses. Then, a fuzzy-adaptive proportional integral controller is specially-designed for the triple closed-loop position-regulation to adapt to the piano tuning applications. Simulation is conducted on a 20 rpm three-phase permanent magnet synchronous motor servo drive-based piano tuning system to validate the proposed piano tuning method and to verify the proposed control techniques.

Closed-Loop Position Control for Growing Robots Via Online Jacobian Corrections

Growing continuum robots offer improved safety and navigation in confined spaces, due to their inherent compliance and ability to conform to highly curved paths. Navigation of these, and other continuum robots, often involves frequent interactions with the surrounding environment, which are typically unknown and can affect the kinematics of the robot. We propose here an approach for controlling continuum robots based on leveraging real-time position and orientation measurements. This pose information is used to update a local model of the robot's velocity kinematics in an online manner via corrective rotations and magnitude adjustments. We combine the proposed control approach with a method for localizing the tip of a growing robot and evaluate the performance of closed-loop position control on a point-reaching task in unconstrained and constrained environments. The closed-loop system achieves an average total error of 3.22 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 1.31 mm in the unconstrained case and 4.56 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 1.56 mm in the constrained case, validating our proposed approach. This work also represents the first method for autonomous position control of growing robots that does not require a map of its environment.

Are nonfragile controllers always better than fragile controllers in attitude control performance of post-capture flexible spacecraft?

This paper addresses the attitude stabilization and vibration suppression problem for post-capture flexible spacecraft subject to external disturbances, model parameter uncertainty, measurement errors, actuator faults, unknown and uncertain inertia, coexisting controller's perturbations of additive and multiplicative types and input constraints. The hybrid nonfragile controller considering the aforementioned multiple complex factors has rarely been reported. In addition, although the nonfragile controller can to some extent tolerate the fragility, the question whether nonfragile controllers are always better than fragile controllers in attitude control performance of flexible spacecraft has never been answered. With these motivations, the aim of this work is to design a hybrid non-fragile controller such that the closed-loop combined attitude system is stabilized, and to test whether nonfragile controllers are always better than fragile controllers in attitude control performance of post-capture flexible spacecraft. Based on the Lyapunov stability theory, the existence condition of such controller is derived in terms of linear matrix inequality. It is worth mentioning that the controller's additive and multiplicative perturbations are accounted for simultaneously. Finally, an illustrative example is given to test the effectiveness of the proposed hybrid non-fragile controller and corresponding fragile controller for comparison.

Modeling and Simulation of Heavy-Lift Tethered Multicopter Considering Mechanical Properties of Electric Power Cable

In case of a fire at a high-rise building which is densely populated, an extension ladder is used to rescue people who have yet to evacuate to a safe place away from the fire, whereas those who are stranded at a height that is unreachable with the ladder should be promptly saved with different rescue methods. In this case, an application of the tethered flight system capable of receiving power over a power cable from the ground to a multicopter may guarantee effective execution of the rescue plan at the scene where fire is raging without any restrictions of the flight time. This article identified restrictions that should be considered in the design of a multicopter capable of tethered flight aimed to rescue stranded people at an inaccessible location with an extension ladder at a fire-ravaged high-rise building and assessed its feasibility. A power cable capable of providing dozens of kilowatts of electricity should be installed to enable the implementation of the rescue mission using the tethered multicopter. A flexible multi-body dynamics modeling and simulation with viscoelastic characteristics and heavy weight of power cable were carried out to evaluate the effects of such cable of the tethered flight system on the dynamic characteristics of the multicopter. The results indicate that as for a heavy-lift tethered multicopter designed to be utilized for rescue operations, the properties of the power cable, such as weight, rigidity and length, have a major impact on the position and attitude control performance.

An active force controlled of small CMG-based satellite

Purpose This paper aims to investigate the attitude control pointing improvement for a small satellite with control moment gyroscopes (CMGs) using the active force control (AFC) method. Design/methodology/approach The AFC method is developed with its governing equations and integrated into the conventional proportional-derivative (PD) controller of a closed-loop satellite attitude control system. Two numerical simulations of an identical attitude control mission namely the PD controller and the PD+AFC controller were carried out using the MATLAB®-SimulinkTM software and their attitude control performances were demonstrated accordingly. Findings Having the PD+AFC controller, the attitude maneuver can be completed within the desired slew rate, which is about 2.14 degree/s and the attitude pointing accuracies for the roll, pitch and yaw angles have improved significantly by more than 85% in comparison with the PD controller alone. Moreover, the implementation of the AFC into the conventional PD controller does not cause significant difference on the physical structure of the four single gimbal CMGs (4-SGCMGs). Practical implications To achieve a precise attitude pointing mission, the AFC method can be applied directly to the existing conventional PD attitude control system of a CMG-based satellite. In this case, the AFC is indeed the backbone for the satellite attitude performance improvement. Originality/value The present study demonstrates that the attitude pointing of a small satellite with CMGs is improved through the implementation of the AFC scheme into the PD controller.