Position Loop Research Articles

Nonlinearity Compensation and High-Frequency Flexibility Suppression Based RIC Method for Precision Motion Control Systems

For precision motion systems widely applied in industrial manufacturing equipments, it is critical to achieve both high trajectory tracking accuracy and superior disturbance rejection ability. In this article, a novel nonlinearity compensation and high-frequency flexibility suppression based real-time iterative compensation (RIC) method is proposed to achieve excellent tracking performance in practice. The unexpected nonlinearity and high-frequency flexible mode of the plant, which limits the achievable control performance, is first compensated and suppressed. Subsequently, a RIC method based on accurate linear prediction model is proposed to further reduce the tracking error by adding a compensation term to the initial reference trajectory. The trajectory compensation idea of RIC is comparative to remarkable iterative learning control (ILC), but the proposed RIC can online generate and adjust the compensation term during real-time motion without abundant offline iteration trials in ILC. This mechanism significantly enhances the robustness to trajectory variations and external disturbances. Comparative experiments carried out on a ball-screw-driven precision motion stage with full-closed loop position feedback validate the effectiveness and superiority of the proposed method for various trajectory tracking tasks. The proposed method outperforms ILC on tracking performance, and possesses the robustness to various disturbances and reference variations, which leads to industrial application significance.

Cascade Control for Two-Axis Position Mechatronic Systems

The current paper proposes an extension for two controller design procedures for a two-axis positioning mechatronic system, followed by a comparison between them. As such, the first method consists in formulating an optimization problem in terms of linear matrix inequalities (LMIs) in order to impose the location of the closed-loop poles, considering an uncertain model of such a system. The uncertain model is treated using various forms of linear differential inclusions (LDIs), namely, polytopic LDI (PLDI) and diagonal norm-bound LDI (DNLDI). Additionally, the problem regarding the command signal constraints is characterized in terms of LMIs. The imposed structure of the controller is a cascade one, with a PI controller for the position loop and a P controller for the velocity loop, having an additional feedforward term. On the other hand, the second method consists in designing a cascade controller with an inner P controller, as in the previous method, the outer controller being a fractional-order IλIDλD (FO–ID) controller. In terms of degrees of freedom, both methods present four degrees of freedom for each axis. The presented controller design procedures will be applied for a numerical example of such a positioning system, and a comparison of the obtained performance metrics will be performed.

Research on Educational Robot System Based on Vision Processing.

Aimed at the poor recognition effect of current educational robots on objects with complex shapes and colors and the single design of related experiments, this paper proposes a robot teaching instrument. The robot adopts a servo motor with an encoder, a drive, and a variety of sensors to realize a motor current loop, speed loop, position loop, and closed-loop control functions. Three experimental schemes were designed: a PID adjustment experiment, a robot obstacle avoidance and object-grasping program writing experiment, and a complex object recognition experiment based on cascade classifiers. The robot is conducive to improving students' self-initiative ability, deepening their understanding of PID closed-loop control, multi-sensor fusion, and deep learning knowledge. It can improve students' programming ability, enabling them to effectively combine theory and practice, as well as to comprehensively apply professional knowledge.

Mesial or distal to canine: Which is better for the position of closing loops? Analysis of tooth movements based on numerical simulation

Although many studies investigating the mechanical behavior of loop mechanics have focused on loop designs to produce a higher moment-to-force ratio, few studies have clarified the effect of loop position on the force system and resultant tooth movements. This study aimed to simulate orthodontic tooth movements during space closure and to compare the effects of loop position in association with different degrees of gable bend on tooth movements using the finite element method. Two finite element models of the maxillary dentition were constructed, with the loop placed mesial or distal to the canine. Tooth movements during loop activation were simulated while varying the degree of gable bend. When the loop was placed distal to the canine, the incisor showed uncontrolled tipping even with the gable bend. Placement of the loop mesial to the canine produced controlled tipping or root movement of the incisor, depending on the degree of gable bend. Placement of the closing loop mesial to the canine in combination with the incorporation of a gable bend into the archwire distal to the canine could provide better control of incisor movements, such as controlled tipping or root movement, as compared with placement of a gable bend into the loop located distal to the canine.

Anti-disturbance Trajectory Tracking Control for a Quadrotor UAV with Input Constraints⋆

This paper presents the trajectory tracking control for a quadrotor unmanned aerial vehicle(UAV) with disturbances and input constraints. The UAV's system is decomposed into an outer position loop and an inner attitude loop. The position tracking control is achieved by a class of saturated proportional-derivative(PD) control laws. Assuming that the unknown disturbances mainly effect on the translational dynamics, an adaptive control term is investigated to compensate the effects of the disturbances. The position tracking control force implies a coupled-attitude system that connects the inner attitude loop with the outer position loop. An intrinsic PD control law, which is directly designed on the special orthogonal group SO(3), is proposed to track the desired attitude. In order to reduce the calculational difficulty of the attitude tracking control law, an observer-based control law is further developed while the control law and observer can be designed separately. Simulation results complete this work.

Адаптивна система управління швидкісним режимом вільної прокатки з нечітким регулятором

The best high-speed mode of rolling mills is the mode of free rolling with loop formation in finishing groups of cages. Stabilization of the loop is carried out by the control system of the rotation frequency of the rolls of rolling cages based on the information of the sensor of the position of the loop. The increase in the loop depends on the frequency of rotation of the rolls of adjacent cages and the coefficient of extraction of the rolled product in the cage following the adjustable gap. To set up the system, it is necessary to know the numerical characteristics of the influences that disturb and affect the size of the rolling loop. The change in the rotation frequency of the main drive of the cages during the stabilization of the size of the rolling loop in the intercellular gap of the cages of the finishing group of the continuous rolling condition was studied. The change in the rotation frequency of the rolls characterizes the total effects of the rolling mode on the size of the loop. Research have shown that in a non-stationary realization it is possible to single out a trend that is described by a completely deterministic dependence, and to conduct an analysis of a random stationary realization with respect to this trend. A structural diagram of the circuit for regulating the position of the rolling loop was developed. This scheme includes: an electric wire with a current loop, a speed loop, a speed regulator, a rolling loop, a loop position regulator, a compensator of disturbing influences. The compensator is based on the Fuzzy controller and produces a control effect depending on the inconsistency in the loop control circuit. In this way, the low-frequency disturbance component at the rolling speed, which can reach 10% of the rolling speed, is monitored and compensated. The obtained data of changes value of the loop without and with a compensating circuit. The size of the loop in the system without a compensating circuit when rolling a thicker rear part of the rolled product reaches the maximum permissible size. This does not happen in a system with a compensating circuit. It is possible to stabilize the value of the loop in a given range either by increasing the regulator coefficient, thereby worsening the dynamics of the entire multi-link control system of the high-speed rolling mode, or by using the proposed method of adaptive disturbance compensation.

Realization of Control Algorithm for Vehicle Optoelectronic Tracking Platform Based on Sliding Mode Control and Active Disturbance Rejection Control Optimized by Differential Evolution Algorithm

In order to improve the tracking ability of the vehicle mounted photoelectric tracking platform, and make its tracking system has the characteristics of rapid response, small overshoot, high-precision position tracking, strong anti-interference and good robustness, In this paper, a joint active disturbance rejection control (ADRC) and sliding mode control (SMC) method is proposed, which can effectively improve the tracking ability of the equipment. Firstly, the mathematical model of the DC motor is analyzed, and then the sliding mode control based on the linear extended state observer (LESO) and the third-order tracking differentiator is established as the speed loop control of the system. Finally, the parameters of the nonlinear ADRC which built control system,s position loop are optimized by the improved differential evolution (DE) algorithm. The speed loop simulation results show that the proposed algorithm has better control effect than PID control algorithm, Robust control algorithm, and ADRC control algorithm; The simulation of position loop demonstrates that the performance of the controller optimized by DE algorithm is better than the parameter tuning based on experience. The experimental results illustrate that the proposed control algorithm can ensure that the Optoelectronic Tracking equipment can track the target which 3km away with 0.1 mrad accuracy.

A Novel Two-Phase Mode Switching Control Strategy for PMSM Position Servo Systems With Fast-Response and High-Precision

In this article, a novel mode switching control (MSC) strategy is proposed containing a fast-response phase and a high-precision settling phase to meet the requirement of high-quality point-to-point permanent magnet synchronous motor servo systems. In the fast-response stage, an adaptive trajectory planning method is developed to program the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis current profile online based on the reference for the motor to reach the neighborhood of the reference position in minimum time. The chattering in the conventional time-optimal control is overcome and the idea that skipping speed and position loop with preplanned <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis current trajectory is first attempted. After switching, the high-precision settling stage that is responsible for improving the transient performance in terms of reducing the overshoot and settling time is built with the proposed robust composite nonlinear feedback (RCNF) control law. This RCNF method cancels the overall disturbance through an extended state observer. The switching condition for the proposed MSC controller is clarified. Afterward, the whole closed-loop system's stability is strictly proved. Experiments are then conducted based on different scenarios to prove the effectiveness and robustness of the proposed MSC method.

Disturbance-Observer-Based Adaptive Fuzzy Tracking Control for Unmanned Autonomous Helicopter With Flight Boundary Constraints

In this article, a disturbance-observer-based adaptive fuzzy tracking control scheme is proposed for a medium-scale unmanned helicopter of six degrees of freedom in the presence of system uncertainties, flight boundary constraints, and external disturbances. A flight boundary protection algorithm is proposed to ensure its flight trajectory within the given safety range. A fuzzy logic system is utilized to estimate the system uncertainties and a nonlinear disturbance observer is adopted to handle the unknown compound terms of the external disturbances and the estimation errors resulting from the fuzzy logic system. An inverse optimal control approach is then used to avoid solving the Hamilton–Jacobi–Bellman equation in minimizing a cost function in the attitude loop. It is shown via the Lyapunov method that the desired safe tracking performance of the position loop and attitude loop of the controlled unmanned helicopter can be achieved. Simulations are provided to illustrate the effectiveness of the proposed control scheme.

PTZ Active Vision Method Based On BEBLID

The traditional pan-tilt-zoom (PTZ) camera relies on manual operation in control, and it requires a large number of samples for training in the algorithm to achieve higher target recognition accuracy. Therefore, we introduce the Boosted Efficient Binary Local Image Descriptor (BEBLID) propose a pedestrian detection and tracking method applied to the PTZ. By extracting image feature points and feature descriptions, we use Support Vector Machines (SVM) to train fewer samples to complete pedestrian detection. Then we input it into kernel correlation filters (KCF) for subsequent tracking, and use its high frame rate to reduce the feedback steps of the PTZ position loop, which reduces the system running time, and then we control the target image to be always locked in the center of the image. Finally, the experiment is carried out, and the whole system can run normally. Under 700 test samples, the detection effect of this algorithm is the highest, reaching 93.00 %, which is 14.57 % and 3.57 % higher than that of Scale-invariant feature transform (SIFT) and Oriented Brief (ORB).

Control of Quadrotor Based on RBF Neural Network Adaptive Fast Terminal Sliding-Mode Strategy

I The purpose of this paper is to propose a fast adaptive terminal sliding mode control method for quadrotor unmanned aerial vehicles (UAVs) under dynamic uncertainties and external interference. Firstly, a complete mathematical dynamics model of a quadrotor UAV is presented. Secondly, a robust dual-loop nonlinear control law for the quadrotor velocity and attitude tracking is designed. Through the introduction of equivalent control inputs, the attitude control channels can be decoupled and attitude stabilized controllers can be designed separately. For velocity tracking and altitude tracking control, coupled controllers are designed to ensure velocity tracking based on the stability of altitude tracking control. The attitude loop adopts RBF neural network sliding mode control, to compensate for model disturbance uncertainty, adjust its gain in real time, and suppress chattering problems. Finally, the experimental results show that the designed controller can not only suppress external interference, but also achieve accurate tracking of the desired flight command.

A flexible RecC surface loop required for Chi hotspot control of RecBCD enzyme.

Escherichia coli RecBCD helicase-nuclease promotes vital homologous recombination-based repair of DNA double-strand breaks. The RecB nuclease domain (Nuc) is connected to the RecB helicase domain by a 19-amino-acid tether. When DNA binds to RecBCD, published evidence suggests that Nuc moves ∼50 Å from the exit of a RecC tunnel, from which the 3'-ended strand emerges during unwinding, to a distant position on RecC's surface. During subsequent ATP-dependent unwinding of DNA, Nuc nicks the 3'-ended strand near 5'-GCTGGTGG-3' (Chi recombination hotspot). Here, we test our model of Nuc swinging on the tether from the RecC tunnel exit to the RecC distant surface and back to the RecC tunnel exit to cut at Chi. We identify positions in a flexible surface loop on RecC and on RecB Nuc with complementary charges, mutation of which strongly reduces but does not eliminate Chi hotspot activity in cells. The recC loop mutation interacts with recB mutations hypothesized to be in the Chi-activated intramolecular signal transduction pathway; the double mutants, but not the single mutants, eliminate Chi hotspot activity. A RecC amino acid near the flexible loop is also essential for full Chi activity; its alteration likewise synergizes with a signal transduction mutation to eliminate Chi activity. We infer that altering the RecC surface loop reduces coordination among the subunits, which is critical for Chi hotspot activity. We discuss other RecBCD mutants with related properties.

Distributed formation-aggregation control algorithm for a cluster of quadrotors

This paper focuses on the solution to a formation-aggregation problem concerned with a cluster of quadrotors. In particular, all the quadrotors are steered towards a target region while reaching an expected formation configuration. However, only a subset of quadrotors, treated as leaders, have access to the projections onto the target region; and in the meantime, each quadrotor just exchanges information with its neighbors. It is assumed that the quadrotors without the knowledge of the target region, treated as followers, are within the convex hull of the leaders in the expected configuration. A distributed formation-aggregation control algorithm is proposed under the hierarchical framework. To be specific, resorting to an auxiliary dynamic system with a distributed idea, a command force is first synthesized in the position loop for the concerned formation-aggregation objective. Next, an applied thrust and a command attitude are extracted from the synthesized command force. Finally, an applied torque is synthesized in the attitude loop such that the attitude tracking to the command one is realized. In terms of the Lyapunov theory, it is shown that the leaders are capable of guiding the overall quadrotor cluster into the target region in the expected configuration. Simulations are carried out to validate the theoretical results.

Safety Control for Quadrotor UAV Against Ground Effect and Blade Damage

This article proposes a safety control scheme for quadrotor unmanned aerial vehicle (UAV) to counteract ground effect and blade damage. The impacts of ground effect and blade damage are quantitatively analyzed in the established model. The proposed safety control scheme consists of position and attitude loops. Specifically, a proportional and derivative controller is designed as a baseline control with acceleration feedforward in the position loop. A disturbance observer (DO) using the measured Euler angles is exploited to estimate the lumped disturbance forces. The developed DO can effectively mitigate the estimation deviation caused by the angle tracking error. Subsequently, differential flatness theory is used to obtain the Euler angle references and the derivatives. In the attitude loop, sliding mode control and fixed-time sliding mode observer (SMO) are integrated to deal with ground effect and blade damage promptly. To demonstrate the effectiveness of the proposed safety control scheme, flight experiments are carried out, where the quadrotor UAV flies close to the rugged ground in the presence of blade damage.

Double-Loop Control for Torque Tracking of Dry Clutch

Torque tracking is an important control target of a dry clutch. At present, the torque tracking control method of a dry clutch generally uses the relationship between the clutch torque and release bearing position obtained via experiment to convert the torque tracking control of the clutch into the position tracking control of the release bearing. However, due to the nonlinearity and time-varying parameters of the dry clutch, it is difficult to obtain an accurate and fixed relationship between torque and position. At the same time, there are also the nonlinearity and interference problems in the position tracking control process. In order to solve the above problems, this paper takes the torque tracking control process of the dry clutch in a three-speed automatic mechanical transmission of an electric vehicle as an example and proposes a double-loop control controller including torque loop and position loop. Firstly, the drive system dynamic model of electric vehicles and clutch actuator dynamic models is established. Secondly, the torque loop controller is established with the adaptive feedforward-feedback control method. The time-varying parameters are adaptively adjusted with adaptive feedforward control to solve the problem of the time-varying relationship between torque and position. In addition, the feedback control loop is added to improve the robustness of the controller. Thirdly, the position loop controller is established with the backstepping-based active disturbance rejection control method to solve the nonlinear and disturbance problems of the position tracking control. In the end, the torque loop and position loop are cascaded to form a double-loop controller, and the torque tracking control simulations of the dry clutch are carried out. The simulation results show that the double-loop controller has good control performance, and the effectiveness of the controller has been preliminarily verified.

Analysis on the Common Quality Problems and Production Methods of Jeans Belt Loop Knot

The belt loop is an important part of a standard five-pocket jeans, integrating functionality and aesthetics. Because of common problems such as skewed belt loop, unequal lengths, improper slackness, double lines at the front pocket of the belt loop cover, exposed bottom of the belt loop, asymmetry, too low or too high position of the belt loop, and no light in the back, we tracked the sewing of the belt loop in the jeans production line, analyzed the causes of the problems, and came out with targeted solutions. We analyzed the operation steps of knotting jeans belt loops and then develop daily maintenance measures for knotting machines, provide technical guidance for seamstresses/seamsters and team leaders to enhance the maintenance ability to knot machines, enhance the ability of knotting machines to run well, ensure the stability of jeans belt loops quality, and provide technical reference for quality control of belt loops in the same type of jeans production lines.

Fixed-time robust trajectory tracking control for quadrotor UAV with disturbances

Trajectory tracking control of nonlinear system with disturbances has been extensively investigated. A novel fixed-time robust trajectory tracking control scheme for quadrotor unmanned aerial vehicle (UAV) with disturbances is proposed in this paper. First, the quadrotor system is split into position and attitude loops. With the purpose of restraining coupling disturbances on position loop forced by imperfect attitude tracking, a novel fixed-time unknown input observer (UIO) is devised to accurately estimate the disturbances, with the unique feature that does not need the upper bound of disturbances or the derivatives. Second, taking unmeasurable velocity and unknown external disturbances into account for attitude loop, a fixed-time extended state observer (ESO) is proposed to precisely observe them within a fixed time. Third, considering control accuracy and convergence rate, robust fixed-time controllers are, respectively, designed for position and attitude loops, and the convergence time of overall system is independent of system initial states. Then, a comprehensive stability proof for the two-loop system is presented with a combination of bi-limit homogeneity and Lyapunov technique. Finally, simulations and comparisons are performed to demonstrate the effectiveness of the designed control scheme.

Design and fabrication of non-resonant PZT MEMS micromirror with buried piezoresistors for closed loop position control

This paper reports on a 1D PZT micromirror integrated with buried piezoresistors for quasi-static feedback position control. The piezoresistors located along or below the PZT actuators could achieve the sensitivity as high as 3.1 mV/°, which was two orders of magnitude higher than the traditional ones located at the torsion springs (8.2 μV/°). This increased the signal-to-noise ratio by 2 orders of magnitude, which could enable the accurate position control. The response of the longitudinal sensors along the beams had a fast settling time less than 1 ms. The average position error was 0.975%, which was much better than that from the conventional shear stress sensor on the torsion bar of 3.1%.

An active disturbance rejection synchronous control strategy based on cross compensation for stepper motor XY platform

In view of the system uncertainty factors and bilateral drive synchronization problems of XY platform driven by stepping motor, on the basis of the mathematical model of single axis servo system, in order to improve traceability and disturbance rejection in X,Y direction, a double loop structure with PID controller as speed loop and active disturbance rejection as position loop is proposed to solve the contradiction between rapidity and overshoot, moreover, an ESO performance analysis method is proposed, and the parameter tuning rules of ADRC is summarized. On this basis, a deviation self-coupling compensation control strategy is proposed to solve the problem of bilateral drive synchronization in axis X direction, and the mechanism and parameter adjusting method of the compensator are studied. The comparative experiment between ADRC+PID+deviation self-coupling compensation and PID+PID+deviation self-coupling compensation, the comparative experiment between ADRC+PID+deviation self-coupling compensation and ADRC+PID are conducted, respectively. Finally, the experiment of synthetic trajectory of X and Y is carried out, the simulation and experimental results demonstrate that the response time of the control strategy proposed in this paper is 0.5 s, which is 0.2 s faster than PID’s, and the disturbance recovery time is 50% of PID control. Therefore, the proposed ADRC+PID+deviation self-coupling compensation control strategy can not only effectively improve the tracking performance of the XY platform system, but also enhance the robustness of the system.

Control of Free Piston Stirling Linear Generator system connected with dc/dc converter for energy storage applications based on SVPWM Rectification Method

Recently, the world has been facing several challenges in terms of environmental change, which is expected to increase in the coming periods. Further challenging is how to reduce the emissions of greenhouse gasses into the atmosphere. Such emissions pollute our atmosphere, resulting in global warming. However, the wide use of renewable energies can both help to fight against this phenomenon and reach long-term goals. Considering the growing global concern over the use of fossil fuels and environmental pollution. In this case, a Stirling engine with diversified heat sources and low pollution was developed, and the Free Piston Stirling Linear Generator (FPSLG), which can be directly connected to the Stirling engine and thus eliminate the need for an intermediate mechanical transmission mechanism, was used to create a power generation system with the Stirling engine and has been employed in a range of applications, including space power supply, solar energy generation, and others. This article models two sets of power converters, one of which is connected to the FPSLG and the other to the storage battery system. The Space Vector Pulse Width Modulation (SVPWM) control methods adaption to the AC/DC rectifier and the two-loop Proportional Integral (PI) control method adaption to the DC/DC converter used for renewable energy conversion is proposed. Furthermore, the traditional PI in the position loop is replaced by a Proportional Resonance (PR) controller to increase the frequency and displacement tracking performance. The linear generator’s control system is simulated, and the efficiency of the proposed control strategy is proven. The system was initially simulated in MATLAB/Simulink using the dq-PI current controller to produce the logic pattern for the Voltage Source Rectifier (VSR), and the resulting logic pattern was examined.