On the Performance of a Nonlinear Position-Velocity Controller to Stabilize Rotor-Active Magnetic-Bearings System

The performance of a nonlinear position-velocity controller in stabilising the lateral vibrations of a rotor-active magnetic-bearings system (RAMBS) is investigated. Cubic nonlinear position-velocity and linear position-velocity controllers are introduced to stabilise RAMBS lateral oscillations. According to the proposed control law, the nonlinear system model is established and then investigated with perturbation analysis. Nonlinear algebraic equations that govern the steady-state oscillation amplitudes and the corresponding phases are derived. Depending on the obtained algebraic equations, the different frequency response curves and bifurcation diagrams are plotted for the studied model. Sensitivity analysis for the linear and nonlinear controllers’ gains is explored. Obtained analytical results demonstrated that the studied model had symmetric bifurcation behaviours in both the horizontal and vertical directions. In addition, the integration of the cubic position controller made the control algorithm more flexible to reshape system dynamical behaviours from the hardening spring characteristic to the softening spring characteristic (or vice versa) to avoid resonance conditions. Moreover, the optimal design of the cubic position gain and/or cubic velocity gain could stabilise the unstable motion and eliminate the nonlinear effects of the system even at large disc eccentricities. Lastly, numerical validations for all acquired results are performed, where the presented simulations show accurate correspondence between numerical and analytical investigations.

Design and control of the first foldable single-actuator rotary wing micro aerial vehicle

The monocopter is a type of micro aerial vehicle largely inspired from the flight of botanical samaras (Acer palmatum). A large section of its fuselage forms the single wing where all its useful aerodynamic forces are generated, making it achieve a highly efficient mode of flight. However, compared to a multi-rotor of similar weight, monocopters can be large and cumbersome for transport, mainly due to their large and rigid wing structure. In this work, a monocopter with a foldable, semi-rigid wing is proposed and its resulting flight performance is studied. The wing is non-rigid when not in flight and relies on centrifugal forces to become straightened during flight. The wing construction uses a special technique for its lightweight and semi-rigid design, and together with a purpose-designed autopilot board, the entire craft can be folded into a compact pocketable form factor, decreasing its footprint by 69%. Furthermore, the proposed craft accomplishes a controllable flight in 5 degrees of freedom by using only one thrust unit. It achieves altitude control by regulating the force generated from the thrust unit throughout multiple rotations. Lateral control is achieved by pulsing the thrust unit at specific instances during each cycle of rotation. A closed-loop feedback control is achieved using a motion-captured camera system, where a hybrid proportional stabilizer controller and proportional-integral position controller are applied. Waypoint tracking, trajectory tracking and flight time tests were performed and analyzed. Overall, the vehicle weighs 69 g, achieves a maximum lateral speed of about 2.37 m s−1, an average power draw of 9.78 W and a flight time of 16 min with its semi-rigid wing.

A Joint-space Position Control-based Approach to Haptic Rendering of Stiff Objects using Gain Scheduling

Haptic rendering often deals with interactions between stiff objects. A traditional way of force computing models the interaction using a spring-damper system, which suffers from stability issues when the desired stiffness is high. Instead of computing a force, this paper continues to explore shifting the focus to rendering an interaction with no penetration, which can be accomplished by using a position controller in the joint space using the encoders as feedback directly. In order to make this approach easily adaptable to any device, an alternative way to model the dynamics of the device is also presented, which is to linearize a detailed simulation model. As a family of linearized models is used to approximate the full dynamic model of the system, it is important to have a smooth transition between multiple sets of controller gains generated based on these models. Gain scheduling is introduced to improve the performance in certain areas and a comparison among three controllers is conducted in a simulation setup.

Nonlinear Position Control with Augmented Observer in Brushless DC Motor

In this paper, position control using both a nonlinear position controller and a current controller with an augmented observer is proposed for a Brushless DC motor. The nonlinear position controller is designed to improve the position tracking performance based on the tracking error dynamics. The current controller is developed to track the desired currents generated from the desired torque, which is calculated based on the nonlinear position controller. The augmented observer is designed to obtain the knowledge of both state variables and disturbance. Closed-loop stability is proven through the Lyapunov theorem. Simulations were performed to evaluate the effectiveness of the proposed method.

Robust Nonlinear Position Control with Extended State Observer for Single-Rod Electro-Hydrostatic Actuator

In the existing literature, studies on position controller design using only position feedback, considering the disturbances for single-rod electro-hydrostatic actuators (EHAs), have not been reported. Herein, we propose a robust nonlinear position control with an extended state observer (ESO) for single-rod EHAs. A new EHA model that consists of position, velocity, and acceleration with an internal state variable is developed. Instead of the separated port pressure dynamics, the acceleration dynamics were defined. The external disturbance, model, and input function uncertainties were lumped into a disturbance. An ESO is developed to estimate the disturbance, as well as the position, velocity, and acceleration. In practice, it is difficult to accurately estimate the disturbance because it includes the external disturbance, system dynamics, and input function uncertainty. The poor estimation performance may degrade the position tracking performance, but a high gain cannot be used to suppress the estimation error because of the measurement noise amplification. To resolve this problem, a robust nonlinear position controller is developed via a backstepping procedure. In the controller, a nonlinear gain is implemented to sufficiently suppress position tracking without the use of a high gain. The stability of the closed-loop system is mathematically proven using the input-to-state stability. The proposed method is simple and suitable for real-time control.

A model-based PID-like motion control method for flexible-joint manipulator with harmonic drives

A novel control method is proposed to achieve high trajectory tracking precision, for flexible-joint manipulators. The method consists of three major parts: joint torque generator, joint torque tracker and motor position controller. The expected torque is generated by a PID controller based on the manipulator’s rigid dynamics model. In the torque tracker, motor position is corrected in both feedback and feedforward ways. Finally, the motor position controller is responsible to track the corrected motor trajectory to achieve the torque and position control. To suppress nonlinear friction, a disturbance observer is also implemented. The method is verified with a seven-DOFs manipulator. Simulation and experimental results show that, the proposed method is efficient and practical to suppress vibration caused by flexible transmission and disturbance due to friction. As result, high positioning accuracy is achieved in a certain wide working speed range. The no-load motion accuracy is better than 0.6 mm with a manipulator whose length is 1.8 meter, and the motion error is less than 3 mm with loading of four kilograms.

Development of a position tracking drive system for controlling PMSM motor using dSPACE 1104-based variable structure

In industrial electric drive systems, it is common to find objects that need to solve the problem of angular position control, moving the object from one position to another asymptotically with no over-correction and guarantee. calculation of maximum fast impact. This is a multi-target optimization problem with many different solutions. This paper presents a method of constructing a PMSM motor position controller with a variable structure using dSPACE 1104 card. The system consists of a position control loop with a variable structure that is an outer loop and a speed control loop degree is the inner loop. In which, the speed adjustment loop uses adaptive law to compensate for uncertain functions and build a sliding mode observation to estimate load torque, friction and noise. The results of the simulation study were verified on Matlab-Simulink environment and experimented on dSPACE 1104 card to check the correctness of the built controller algorithm. The research results in the paper are the basis for the evaluation and setting up of control algorithms, design of electric drive systems in industry and the military.

Electromechanical guidance system based on a fuzzy proportional-plus-differential position controller

Purpose. The purpose is to develop solutions for the implementation of optimal laws of arms positioning, overshoot-free and requiring no post-adjustments. Method. The control model is based on the fuzzy set theory; and the structural modeling methodology is used to study the dynamics indices. Results. The structural scheme of the positional electromechanical system with a fuzzy proportional-plus-differential position controller and the method of control adaptation to the position reference signal change are obtained. Scientific novelty. A model of a fuzzy proportional-differential controller signal adaptation in the structure of a positional electromechanical system is proposed. Practical value. A solution is obtained for the implementation of optimal guidance process, non-overshooting and requiring no post-adjustments, also featuring the maximum weapons speed and minimal sensitivity to parametric disturbances.