Position Control Loop Research Articles

FPGA-based neural fuzzy controller design for PMLSM drive

Based on the technology of field programmable gate array (FPGA), a realisation of fuzzy control (FC) system with radial basis function neural network (RBF NN) tuning is presented to a permanent magnet linear synchronous motor (PMLSM) drive in this paper. Firstly, a mathematic model of the PMLSM drive is defined; then to increase the performance of the PMLSM drive system, an FC constructed by a fuzzy basis function and its parameter adjustable mechanism using RBF NN is applied to the position control loop of the PMLSM drive system to cope with the effect of the system dynamic uncertainty and the external load. Secondly, FPGA by using finite state machine (FSM) method is presented to realise the aforementioned controllers, and VHSIC hardware description language (VHDL) is adopted to describe the circuit of the FSM. Finally, an experimental system is established to verify the effectiveness of the proposed FPGA-based neural fuzzy control system for PMLSM, and some experimental results are confirmed theoretically.

Model-Based Feedforward Control of Large Deformable Mirrors

In this paper, a model-based feedforward control concept for fast set-point changes of large deformable mirrors is proposed. It takes into account local position control loops of excited actuators and mode-dependent stiffness variations of the mirror shell. Based on partial differential equations for the temporal and spatial behavior of the deformable mirror, a modal approximation of the mirror dynamics is performed. It is shown that a second order approximation of the eigenmode dynamics is appropriate for low-order modes even when additional system components as delays, digital-to-analog converters, current drivers, actuator-magnet efficiencies, capacitive sensors, and analog-to-digital converters are included. In particular, appropriate transfer functions with identified coefficients of the proposed modal models are presented for a 45-actuator prototype of the Large Binocular Telescope adaptive secondary mirror (P45). Additionally, experimental results with model-based feedforward control are presented. The identified dynamic model of the P45 is finally used to derive flatness based feedforward commands for chopping.

Contour Following Using C2 PH Quintic Spline Curve Interpolators

AbstractThis paper presents a C2 Pythagorean-Hodograph (PH) spline curve interpolator for contour-following tasks. To generate the C2 PH quintic spline curve, a uniform knot sequence is employed. The S-curve motion planning architecture with variable feedrate for a planar C2 PH quintic spline curve is also developed. In particular, C1 cubic feed acceleration/deceleration is imposed on the first and last PH quintic spline segments. The proposed interpolation algorithm along with a simple position loop controller is employed to perform a closed C2 PH quintic spline curve following task. Experimental results indicate that the proposed interpolator is not only feasible for machining the complicated parametric curves represented in C2 PH quintic spline form but also yields satisfactory contouring performance for variable feedrate control.

Attitude Controller Design and Test of Korea Space Launch Vehicle-I Upper Stage

This paper introduces the upper stage attitude control system of KSLV-I, which is the first space launch vehicle in Korea. The KSLV-I upper stage attitude control system consists of two electro-hydraulic actuators and a reaction control system using cold nitrogen gas. A proportional, derivative, and integral controller is designed for the electro-hydraulic thrust vectoring system, and Schmidt trigger ON/OFF controllers are designed for the reaction control system. Each attitude controller is designed to have enough stability margins. The stability and performance of KSLV-I upper stage attitude control system is verified via hardware in the loop tests. Hardware in the loop tests are accomplished for perturbed flight conditions as well as nominal flight condition. The test results show that the attitude control loop of KSLV-I upper stage is very stable and the attitude controllers perform well for all flight conditions. Attitude controllers designed in this paper have been successfully applied to the first flight of KSLV-I on August 25, 2009. The flight test results show that all attitude controllers of the KSLV-I upper stage performed well and satisfied the accuracy specifications even during abnormal flight conditions.

Indoor Hovering Control of Small Ducted-fan Type OAV Using Ultrasonic Positioning System

This study focused on a development of attitude stabilization and a position (hovering) control scheme of the SFR (Small Flying Robot). The platform type of the SFR is a ducted-fan type OAV having a diameter of 30 cm. The attitude of the SFR was successfully stabilized by a PD control method. In the attitude control loop, the feedback states were angle and angular rates, which were outputs from an AHRS (Attitude Heading Reference System). The position of the SFR was controlled precisely by the LQI (Linear Quadratic Integration) method with a Kalman filter. In the position control loop, an ultrasonic positioning system was used for the 3D position reference, which was developed in a previous research. The proposed simple mathematical model could analyze dynamics and stability of the SFR. Also, the stabilities of the attitude control and the precision of the position control were verified by comparing and analyzing data of experiments and simulations.

Trajectory tracking controller design using neural networks for a tiltrotor unmanned aerial vehicle

This article presents a design of trajectory tracking controller for a tiltrotor unmanned aerial vehicle (UAV). The objective of this design is to control the tiltrotor aircraft with one fixed controller architecture for all flight modes, viz. helicopter mode, conversion mode, and aeroplane mode. The controller is implemented using two time-scale separations, and thus comprises an inner loop for attitude control and an outer loop for trajectory control. The dynamic model inversion (DMI) technique is applied to both the control loops such that the inner-loop and the outer-loop DMIs are driven using the angular equations of motion and the translational equations of motion, respectively. In addition, online adaptive neural networks are employed to compensate for the model inversion errors of the inner loop and the outer loop due to the lack of complete knowledge of tiltrotor aircraft dynamics. The pseudo-control hedging algorithm is adopted to reduce the instability problem caused by the time-delay of control loops, saturation, and rate limit of actuators. The trajectory tracking controller is evaluated using a sophisticated six-degree-of-freedom non-linear simulation programme with an approach and landing scenario including all flight modes of a smart UAV, a tiltrotor UAV.

Forward kinematics modelling of a parallel ankle rehabilitation robot using modified fuzzy inference

This article deals with forward kinematics (FK) mapping of a parallel robot, especially designed for ankle joint rehabilitation treatments. Parallel robots exhibit highly coupled non-linear motions hence conventionally a unique closed form solution of their FK cannot be obtained. However, since FK is a key module in closed loop position and force control, its accurate and fast solution is indispensable. To solve the FK problem, a modified fuzzy inference system (FIS) is proposed in this paper for the first time which is time efficient and becomes very accurate when its parameters are optimized. In the proposed work, FIS has been optimized using three approaches namely: gradient descent (GD), genetic algorithm (GA) and modified genetic algorithm (MGA). The FIS, optimized by MGA has been found to be more accurate than the GD and GA optimized FIS. Performance of the MGA based fuzzy system has been found better both in terms of accuracy and computation time, when compared with Newton–Raphson iterative method and other fuzzy and neural approaches.

Pseudo-Periodic Encryption of Extended 2-D Surfaces for High Accurate Recovery of any Random Zone by Vision

This article presents a binary position encoding method for extended two-dimensional surfaces. Position encryption is based on linear feedback shift register sequences inserted within a periodic frame of spots. The position and orientation of any local view is retrieved accurately with respect to the encrypted surface. Image processing combines phase computations with binary image feature analysis. Measurement resolution is in the range of 10−2 pixel in position and 10−3 degree for in-plane orientation. The method is used as a visual sensor in a position control loop applied to fluorescence optical microscopy for the recovery of cells of interest within culture dishes.

Forced dynamics control of PMSM drives with torsion oscillations

PurposeThe purpose of this paper is to discuss the design and verification of a new control algorithm for the drive with permanent magnet synchronous motor (PMSM) and flexible coupling based on “Forced dynamics control”. Control laws are derived and tested for the rotor and load angle control and achieve non‐oscillatory position step response with a specified settling time.Design/methodology/approach“Forced dynamics control” is a new control technique based on feedback linearization which forces rotor or load position to follow demanded position with prescribed closed‐loop dynamics. The proposed control structure is developed in two steps: first, the feedback linearisation is applied to the rotor speed and then similar technique is used for position control loop.FindingsThe proposed controller is of the cascade structure, comprising an inner speed control loop, respecting vector control principles and outer position control loop designed to control the rotor or load angle, respectively. Estimates of load torques acting on the motor and load side as inputs of control algorithms are produced in observers and used to compensate disturbances offering a certain degree of robustness. Preliminary experiments confirm that proposed system follows the ideal closed‐loop dynamics with moderate accuracy.Research limitations/implicationsThe focus is on experimental verification of the position control of flexible PMSM drive with two position sensors and moderate precision, where the oscillations due to hardware setup, achieved sampling frequency and corresponding observers adjustment are limited up to 50 rad s−1.Practical implicationsThe designed control structure can substantially improve control performance of industrial plants subjects to torsion oscillations.Originality/valueExperimental results of a novel control structure for the PMSM drives with torsion oscillations are sufficiently promising and confirmed that the rotor and load angle responses follow the prescribed ones fairly closely.

Vibration suppression control for a dies-driving spindle of a form rolling machine using a model-based control with a rotational speed sensor

This paper deals with a control technique of eliminating the transient vibration generated in a dies-driving spindle of a form rolling machine. This technique is based on a model-based control with a rotational speed sensor. A rotational speed sensor is installed in a driven gear part. A control model is composed of a reduced-order mechanical model. The performance of this vibration suppression control method in the velocity control loop is examined by simulations and experiments. Further, the effectiveness of the model-based control integrated into the position control loop is verified by simulations. Simulations and experiments show satisfactory control results.

Predictive Direct Power Control of Three-Phase Pulsewidth Modulation (PWM) Rectifier Using Space-Vector Modulation (SVM)

In this paper, we present a direct power control (DPC) of three-phase pulsewidth modulation rectifier with constant switching frequency using space-vector modulation (SVM). The developed DPC scheme is based on the predictive control strategy to achieve direct control of instantaneous active and reactive power of the converter. For this purpose, at the beginning of each switching period, the required rectifier average voltage vector allowing the cancellation of active and reactive power tracking errors, at the end of the switching period, is calculated by means of predictive control algorithm in the sense of deadbeat control. The main advantages of the proposed control, compared to the works published in this subject, are that no need to use predefined switching table and voltage vector or virtual flux position, PI-based active and reactive power control loops are not necessary and constant-switching frequency. The proposed predictive direct power control was tested both in simulations and experimentally and compared with DPC using switching table. Results have proved excellent performance, and verify the validity of the proposed DPC scheme, which is much better than conventional DPC using switching table.

Implementation of an adaptive position control system of a permanent-magnet synchronous motor and its application

This study proposes an adaptive backstepping controller design for a position control system of permanent-magnet synchronous motors (PMSMs). The proposed system has good performance, including fast transient responses, good steady-state responses and good tracking responses. Based on a proper Lyapunov function, an adaptive backstepping position controller can be systematically developed. In addition, a notch filter is used in the current loop to reduce the limit cycles of the motor current. The control algorithm is implemented by using a Renesas digital signal processor. As a result, the hardware is very simple. The proposed control system includes a position-loop controller and a current-loop controller. All control loops are executed by the digital signal processor. Several experimental results are shown to validate the correctness and feasibility of the proposed control algorithms. The system can achieve a precise position control. In fact, a ball-screw table and a knitting machine have been applied to evaluate the performance of the control system. The study provides a new direction in the use of an advanced control technique in PMSMs and investigates its real industrial applications.

Motion control of the 2-DOF parallel manipulator of a hybrid machine tool

SUMMARYThis paper focuses on the motion control of the two-degree-of-freedom (2-DOF) planar parallel manipulator of a hybrid machine tool. On the basis of the performance analysis of the kinematic control system, a parameter-tuning method is proposed for regulating the control parameters. To improve the response performance, the proportional-derivative control and a low-pass filter are introduced to the position-loop controller. The simulation shows that the response speed is increased and that the tracking error is reduced. Furthermore, the effect of load torque on the contour error is investigated, and the dynamic feedforward control is used to control the parallel manipulator. On the basis of the principle of dual-channel compensation, the feedforward compensator is designed. The simulations, that the moving platform moves along a linear trajectory and circular trajectory, show that the dynamic feedforward control can reduce the effect of load torque on contour error.

System Design and Control of Anthropomorphic Walking Robot LOLA

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper presents the 25-DOF full-size humanoid robot <emphasis emphasistype="italic">LOLA</emphasis> . Our goal is to realize fast and human-like walking. Furthermore, we want to increase the robot’s autonomous, vision-guided walking capabilities. <emphasis emphasistype="italic">LOLA</emphasis> is characterized by a redundant kinematic configuration, an extremely lightweight design, joint actuators with brushless motors and an electronics architecture using decentralized joint control. Special emphasis was put on an improved mass distribution to achieve good dynamic performance. Center of mass trajectories are calculated in real-time from footstep locations using a spline collocation method. Reference trajectories are modified by a stabilizing control system based on hybrid force/position control with an inner joint position control loop. </para>

A new inverse controller for servo‐system based on neural network model reference adaptive control

PurposeThe purpose of this paper is to develop a new inverse controller for servo‐system position tracking control based on neural network (NN) and model reference adaptive control (MRAC).Design/methodology/approachFirst, the model of general servo‐systems is analyzed. Then, a MRAC based on neural network control (NNC) is proposed with mathematical prove of stability. In addition, several simulation cases and experiments are listed to verify the usability of the control scheme.FindingsThis scheme consists of an MRAC, an online NN controller and a robust controller in velocity‐loop. For reducing influence which arose from modeling error, unknown model dynamics, parameter variation, and load changes, the NN controller is introduced to counteract the various influence mentioned above dynamically. MRAC, NNC, and robust controller adjust system to track the approximate velocity‐loop reference model. In this way, the position‐loop is not sensitive to the disturbance on velocity‐loop, and the whole velocity‐loop can be treated as a simple linear model when designing the other parts of the system. In addition, a novel inverse control method based on linear velocity signal filter is introduced to this scheme. In this case, the MRAC, NNC, and robust controller perform as an adaptive inverse controller, which keeps the velocity signal tracking the position loop controller output.Originality/valueThe paper presents a new inverse controller with NNC and MRAC which is practical and flexible.

A Study on the Effects of Servovalve Lap on the Performance of a Closed - Loop Electrohydraulic Position Control System

This paper deals with a closed–loop position control of a double acting and double–rod actuator using an electrohydraulic servovalve (EHSV). This system is studied by using symmetric critical center spool valve (zerolapped) and open center spool valve (underlapped). The nonlinear dynamic behavior of each case is undertaken and simulated. The system is modeled by using five state variables (piston position, piston velocity, actuator pressures, and servovalve spool displacement) and is tested under different step inputs. The EHSV is modeled with a first order differential equation. The closed-loop system stability is investigated by introducing equilibrium state into Jacobian matrix and determining the eignvalues. Viscous friction and compressibility of oil are included in the modeling of the system. Because the electrohydraulic position servo system is not very sensitive to coulomb friction and piston leakage they are neglected. The work showed that when the underlapped servovalve operates in the underlap region, the hydraulic position control system has more stable operation and better transient responses. Keywords: Zerolap, Underlap, EHSV, Steady-State Characteristics, Dynamic Response, Position Control, Modeling, Simulation.

A Real-Time Tool Positioning Sensor for Machine-Tools

In machining, natural oscillations, and elastic, gravitational or temperature deformations, are still a problem to guarantee the quality of fabricated parts. In this paper we present an optical measurement system designed to track and localize in 3D a reference retro-reflector close to the machine-tool's drill. The complete system and its components are described in detail. Several tests, some static (including impacts and rotations) and others dynamic (by executing linear and circular trajectories), were performed on two different machine tools. It has been integrated, for the first time, a laser tracking system into the position control loop of a machine-tool. Results indicate that oscillations and deformations close to the tool can be estimated with micrometric resolution and a bandwidth from 0 to more than 100 Hz. Therefore this sensor opens the possibility for on-line compensation of oscillations and deformations.

FPGA Realization of an Adaptive Fuzzy Controller for PMLSM Drive

This paper presents a hardware realization of an adaptive fuzzy controller (AFC) for a permanent-magnet linear synchronous motor (PMLSM) drive system based on the field-programmable gate-array (FPGA) technology. First, a mathematics model of the PMLSM drive is defined; then, to increase the performance of the PMLSM drive system, an AFC constructed by a fuzzy basis function and a parameter-adjustable mechanism is applied to the position-control loop of the PMLSM drive system to cope with the effect of the system dynamic uncertainty and the external load. A point-to-point (PTP) motion trajectory designed with the trapezoidal velocity profile is considered to smooth the move of the PMLSM at the start and stop conditions. Second, a finite-state machine (FSM) joined by a multiplier, an adder, a lookup table, and some comparators and registers is presented to model the overall AFC, and a VHSIC hardware description language is adopted to describe the circuit of the FSM. In addition, a Nios II embedded processor is used to implement the function of the PTP motion-trajectory algorithm by software. Finally, an experimental system is established to verify the effectiveness of the proposed FPGA-based AFC and the PTP motion-control system, and some experimental results are confirmed theoretically.

Improving dynamic performances of PWM-driven servo-pneumatic systems via a novel pneumatic circuit

In this paper, the effect of pneumatic circuit design on the input–output behavior of PWM-driven servo-pneumatic systems is investigated and their control performances are improved using linear controllers instead of complex and costly nonlinear ones. Generally, servo-pneumatic systems are well known for their nonlinear behavior. However, PWM-driven servo-pneumatic systems have the advantage of flexibility in the design of pneumatic circuits which affects the input–output linearity of the whole system. A simple pneumatic circuit with only one fast switching valve is designed which leads to a quasi-linear input–output relation. The quasi-linear behavior of the proposed circuit is verified both experimentally and by simulations. Closed loop position control experiments are then carried out using linear P- and PD-controllers. Since the output position is noisy and cannot be directly differentiated, a Kalman filter is designed to estimate the velocity of the cylinder. Highly improved tracking performances are obtained using these linear controllers, compared to previous works with nonlinear controllers.

Humanoid robot Lola: Design and walking control

In this paper we present the humanoid robot LOLA, its mechatronic hardware design, simulation and real-time walking control. The goal of the LOLA-project is to build a machine capable of stable, autonomous, fast and human-like walking. LOLA is characterized by a redundant kinematic configuration with 7-DoF legs, an extremely lightweight design, joint actuators with brushless motors and an electronics architecture using decentralized joint control. Special emphasis was put on an improved mass distribution of the legs to achieve good dynamic performance. Trajectory generation and control aim at faster, more flexible and robust walking. Center of mass trajectories are calculated in real-time from footstep locations using quadratic programming and spline collocation methods. Stabilizing control uses hybrid position/force control in task space with an inner joint position control loop. Inertial stabilization is achieved by modifying the contact force trajectories.