Servo Control Research Articles

LabVIEW-based servo valve dynamic and static test system

As a key component of the electro-hydraulic servo control system, the electro-hydraulic servo valve’s performance directly affects the stability of the system’s operation. Therefore, according to the company’s requirements, a servo valve testing system was designed based on LabVIEW. Firstly, the hydraulic system was designed according to the dynamic and static testing requirements of the servo valve. Then, the electrical control system and software system were designed based on PLC and LabVIEW. Finally, dynamic and static characteristic tests of the servo valve were conducted on the designed test bench. A flow-pressure dual closed-loop steady-state control method for testing the no-load flow characteristics was proposed, effectively improving the testing accuracy and meeting the company’s requirements.

Design and development of the deep-rock in-situ condition-preserved coring calibration platform

To systematically validate and calibrate the theory and technology of the deep in-situ condition-preserved coring, the in-situ conditions at different depths should be simulated, and the full-size coring tests should be carried out in this simulated environment. Therefore, a deep-rock in-situ condition-preserved coring calibration platform was designed and developed. The self-tightening sealing structure and the quick-disassembly structure were designed on the basis of an innovative segmented nonuniform-diameter structure, which was a breakthrough from the traditional high-pressure vessel frame and was verified by finite element simulation and actual testing under extreme working conditions, respectively. To simulate the actual deep in-situ environment with a temperature of 150 °C and pressure of 140 MPa for a large Φ450 mm×H1400 mm core, temperature and pressure control systems were designed by coupling, and a pre-embedded high-pressure-resistant temperature sensor was designed. Finally, high-precision assembly automation, complex movement coordination of the coring device with the platform, and rotary dynamic sealing were achieved by utilizing the combination of adaptive cabin body servo control and an adaptive mechanical structure in a limited space, laying a solid foundation for the calibration of in-situ condition-preserved coring.

Brushless Motor FOC Control Method for Robot Arm

With the development of modern industry, more stringent requirements are put forward for the servo control of the mechanical arm, especially the problems of insufficient precision, insufficient dynamic response and poor anti-interference ability. This paper takes the permanent magnet synchronous motor of permanent magnet synchronous motor (PMSM) as the research object, combines the RBF neural network with PID control to improve the traditional magnetic field vector control, improve the lag and dynamic response of traditional PI control, improve the stability of the control system; and introduces the online supervision mechanism to make the control system has good environmental adaptability and adaptive adjustment ability. The experimental results show that the magnetic field vector control algorithm based on RBF-PID has faster response time, higher accuracy and stronger anti-interference ability.

Preliminary experimental study on a servo control strategy for dry electrical discharge machining

Preliminary experimental study on a servo control strategy for dry electrical discharge machining

Designing and Modelling of Pivotal Friction Compensator of Actuator of Hard Disk Drives

Nowadays, hard disk drives are one of the most common devices for storing data. The growing demand for storing the bulk amount of data and retrieving the data as fast as possible from hard disk drives (HDDs) has posed manufacturers with various challenges. To overcome these hurdles different methods, techniques, and control systems are developed to improve the transient response of the HDDs. The transient response of a system is characterized by numerous specifications such as overshooting, peak time, settling time, delay, and rise time. This can also be achieved by using several stages of actuators servomechanism that can also help us to store a large amount of data, it also helps to increase the accuracy of head-positioning of the actuator that eventually leads to enhancement of the transient response of hard disk drives (HDDs). By increasing the accuracy of read/write head actuator there is a challenge to cater the friction at pivot of actuator. This friction can significantly reduce the speed of the actuator and that ultimately leads to the reduced transient responses of the system. This paper aims to design a new modelled-base friction compensator for the servo control of hard disk drives that can improve the transient response of HDDs. Thus, improving the transient responses of HDDs can make the computer more efficient than ever and can save a lot of time while making complex calculations. To achieve this aim measured and replicated responses will be used as guidance and the friction design of HDD will iteratively improve. This can be done by feeding the measured friction forces back to the voice coil motor (VCM) so that the frequencies of the actuator’s head and current be linearized. This proposed design will help in the cancelation scheme and the model-based compensator will be implemented. By improving the tracking seek of HDDs we can also write the data much faster on the HDD and by using numerous techniques we can store a large amount of data on HDDs. Our aim is also to integrate a PID controller into our control system so that we can improve the transient response as much as possible. Our work can be considered important as there are very few frictions compensator control designs that have integrated the PID controller. We are aiming to achieve a significantly improved pivotal friction compensator that can help us to achieve improved transient response of the hard disk drive (HDD).

Accurate prediction method for a microstructure profile based on the force–displacement coupled servo model

Microstructures of specified shapes have been widely applied in electronics, communication, optics, avionics, medical science, and the automotive field. The ultraprecision single-point diamond turning lathe is a core instrument used in microstructure preparation. As a key technical indicator of an ultraprecision lathe, the servo control accuracy of a system directly affects the machining accuracy of the lathe. Because the profile error of microstructures machined by the slow tool servo of the ultraprecision lathe is at the micrometer level, any disturbance reduces the accuracy of parts machining. This paper proposes a tracking error prediction model based on the force–displacement coupled servo model to study the mechanism of action for the cutting force disturbance on a servo control system. The repeated positioning error of an ultraprecision lathe’s linear axis is added to the force–displacement coupled servo model to propose a more practical profile error prediction model and analyze the effect of the cutting force on the part profile. The experimental results indicate that the force–displacement coupled servo tracking error and profile error prediction model proposed in this paper is more accurate than the existing tracking error modeling method without cutting force disturbance. In addition, this paper analyzes how the cutting force in ultraprecision machining affects the servo system and part profile, which provides a reference for subsequent ultraprecision lathe error analysis and improved machining accuracy.

Hardware-in-the-loop setup for contactless skin servo control of neonatal incubators

Infant incubators are used to provide an optimal microclimate for premature infants who are thermally instable. Care in the incubator is stressful for the newborn, therefore, current research aims at establishing contact-free monitoring using infrared thermography, thus, improving comfort and reducing skin contact. The skin temperature can already be controlled automatically in current incubators by using adhesive temperature sensors, resulting in possible irritations and damages to the infant’s skin.In this work, a hardware-in-the-loop test bench was developed to test the interaction of all components necessary for skin temperature control with contactless skin temperature measurement. Accordingly, we designed a setup which can control the incubator, the contactless measurement setup, and a thermal neonate phantom. This offers the possibility to test skin temperature controllers immediately in a closed loop and easily simulate physiological and pathological scenarios.After setting up the test bench, the control systems considered were modeled and identified. Subsequently, initial controllers were designed and validated. We recalled that open incubator hand ports have long been considered a significant disturbance for temperature control. Hence, the performance of the current disturbance rejection in the given incubator setting was investigated. Subsequently, a change of the patient’s metabolism was simulated as a specific challenge.In our case, all controllers investigated were able to stabilize the skin temperature compared to the open-loop case. In the future, the presented hardware-in-the-loop concept will help to design and sufficiently validate skin temperature controllers for subsequent clinical trials.

Nonlinear position control of electro-hydraulic servo system based on lyapunov robust integral backstepping controller

In electro-hydraulic servo systems (EHSS), high nonlinearity and time-varying features limit the hydraulic actuator performance. In feedback-based systems, linearization reduces nonlinearities. Their cancellation may produce instability when modeling uncertainty exists. This work uses a robust nonlinear controller based on Lyapunov theory to control the nonlinear position of the electro-hydraulic servo system (EHSS). The dynamics of the system were modeled as extensively as possible, and then a simplified mathematical model based on the EHSS dynamics was created for the controller design. Integral backstepping was used to design the nonlinear robust controller utilizing the Lyapunov theory of nonlinear systems. Lyapunov functions theoretically ensured closed-loop stability. Comparative simulation analysis and experimental investigation in real-time with the proportional integral derivative (PID) controller optimized offline for position tracking control were carried out. Besides tracking performance and steady-state error, the mean square error (MSE), the root mean square error (RMSE), the maximum absolute value of tracking errors and the standard deviation of tracking errors (σ) was utilized to evaluate the controllers’ performance. The simulation analysis and experimental verification were accomplished under various sinusoidal trajectories using different testing conditions (amplitudes, frequencies, and external disturbance), in all testing conditions the effectiveness of the robust nonlinear integral backstepping controller was demonstrated.

Model-based robust servo control for permanent magnet synchronous motor with inequality constraint

Based on the dynamic model, a robust constrained control method for permanent magnet synchronous motor (PMSM) is proposed in this paper to achieve better trajectory tracking performance. Firstly, the constrained output variable of PMSM is transformed into unconstrained output variable by the monotone unbounded property of tangent function. After conversion, regardless of the uncertainty, the output angular displacement of PMSM always remains within the boundary. In addition, after state transformation of control variables, a new dynamic model of the system is obtained. Secondly, based on the new dynamic model, a control method based on model and error is proposed. Theoretical analysis shows that the proposed control satisfies the requirements of uniformly bounded and uniformly bounded limits. Thirdly, the practicability and effectiveness of the robust controller are verified by simulation and experiments. This method can restrain the influence of uncertainty well and improve the servo performance and operation reliability of PMSM significantly.

Neural network-based finite-time command-filtered adaptive backstepping control of electro-hydraulic servo system with a three-stage valve

This paper aims to improve the tracking control performance of the three-stage valve (TSV) controlled electro-hydraulic servo system (EHSS) with parameter uncertainties and other lumped unknown nonlinearities, including unknown dynamics and disturbances. A more accurate nonlinear model of the TSV-controlled EHSS is established and a neural network-based finite-time command-filtered adaptive backstepping control (NNFCABC) method is proposed for the EHSS. Adaptive control is used to deal with the system parameter uncertainties, and the radial basis function neural network (RBFNN) algorithm is introduced to approximate the lumped unknown nonlinearities. The prediction errors of serial-parallel estimation models (SPEMs) and the tracking errors are utilized together to design adaptive laws to estimate the system parameters and the weights of the RBFNNs. The entire control framework utilizes command-filtered control and backstepping techniques. By applying Levant differentiators as command filters and introducing fractional power terms into the virtual control laws and the SPEMs, the proposed NNFCABC theoretically guarantees the tracking performance of the closed-loop control system with finite-time convergence. Comparative simulations and experiments verify the feasibility and superiority of the proposed control scheme.

The Design of a Tracking Controller for Flexible Ball Screw Feed System Based on Integral Sliding Mode Control with a Generalized Extended State Observer

This article proposes a servo control strategy for compensating matched and mismatched perturbations in flexible ball screw feed systems to improve their tracking performance. The perturbations that satisfy or dissatisfy the matching conditions include external disturbances, parameter uncertainties, and unmodeled dynamics. The flexible ball screw feed model includes both a rigid body and first-order axial structural dynamics. A generalized extended state observer is adopted to observe the matched and mismatched perturbations and various state variables of the system, and an improved integral sliding mode controller is proposed that can simultaneously compensate for the perturbations of the system that satisfy and dissatisfy the matching conditions. In addition, vibration compensation is designed for first-order axial vibration of the system to develop a controller that can quickly and accurately track the ideal reference trajectory, suppress system structural vibrations, and be robust to time-varying uncertainties and external disturbances. Finally, the tracking performance, anti-interference performance, and vibration suppression performance of the designed controller are verified via simulation and comparative experiments.

A novel data acquisition approach for valves in industrial refrigeration

In this paper, a novel method is introduced for the acquisition and transmission of critical parameters from valves used in industrial refrigeration. The parameter sensing provides local intelligence to the valve, which can be later used as a feedback signal for the controller. The hardware design includes ICS (Industrial Control Servo) valve with modifications to connect a Linear Variable Transformer (LVT) position sensor, pressure and temperature sensors. Also, a circuit board carrying the phase shift oscillator, Root Mean Square (RMS) to Direct Current (DC) converter, power supply and a dedicated Bluetooth Low Energy (BLE) module for transmitting the collected data is designed. The transmitted data can be received in a mobile phone android application and used for a secondary data calculation, alarm notification and alerting service technician. The sensor integration along with BLE connectivity creates a novel platform for data acquisition in Industrial Refrigeration (IR). The proposed method tested in real time to regulate the Helium gas flow rate and measured valve parameters is monitored by the dedicated mobile application.

Cross‐entropy‐based adaptive fuzzy control for visual tracking of road cracks with unmanned mobile robot

AbstractVisual tracking of road cracks in unstructured road environment was, is, and remains a crucial and challenging task, which plays a vital role in accurate crack sealing for automated road cracks repair. However, many problems have not been well solved in existing automated road cracks repair, such as the low automation due to partial dependence on manual and the interrupted traffic flow caused by the heavy equipment used. In this article, a cross‐entropy‐based adaptive fuzzy control (CEAFC) method is proposed, which reaches visual tracking with unmanned mobile robot (VT‐UMbot) for road cracks. Specifically, the CEAFC method uses cross‐entropy optimization iteration to tune parameters for the tracking controller, and fuzzy logic is constructed to explore robustness improvement. Moreover, a framework of VT‐UMbot based on a four‐wheel independent differential drive is established, and visual servo and tracking control are integrated into the system. Our experiment shows that the proposed method is extensively evaluated on three road cracks scenarios and achieves state‐of‐the‐art performance with high efficiency.

Parametrization and Optimal Tuning of Constrained Series PIDA Controller for IPDT Models

The new modular approach to constrained control of higher-order processes with dominant first-order dynamics using generalized controllers with automatic resets (ARCs) is addressed. The controller design is based on the multiple real dominant pole (MRDP) method for the integrator plus dead time (IPDT) process models. The controller output constraints are taken into account by inserting the smallest numerator time constant of the controller transfer function into the positive feedback loop representing the automatic reset (integral) term. In the series realization of the proportional–integral–derivative–acceleration (PIDA) controller (and other controllers with even derivative degree), the time constant mentioned is complex, so only the real part of the time constant has been used so far. Other possible conversions of a complex number to a real number, such as the absolute value (modulus), can be covered by introducing a tuning parameter that modifies the calculated real time constant and generalizes the mentioned conversion when designing controllers with constraints. In this article, the impact of the tuning parameter on the overall dynamics of the control loop is studied by simulation. In addition, an evaluation of the stability of the closed-loop control system is performed using the circle criterion in the frequency domain. The analysis has shown that the approximation of the complex zero by its real part and modulus leads to a near optimal response to the set point tracking. The disturbance rejection can be significantly improved by increasing the tuning parameter by nearly 50%. In general, the tuning parameter can be used to find a compromise between servo and regulatory control. The robustness and applicability of the proposed controller is evaluated using a time-delayed process with first-order dominant dynamics when the actual transfer function is much more complicated than the IPDT model. A comparison of the proposed MRDP-PIDA controller with series PI, PID and PIDA controllers based on a modified SIMC method has shown that the MRDP-PIDA controller performs better than the SIMC method, although the SIMC uses a more complex process model.

Adaptive neural approximated inverse control for photovoltaic power generation servo systems with all states constrained

For PV power generation servo systems with motor hysteresis, an all-state constrained decentralized adaptive approximation inversion control strategy is suggested in order to further increase the tracking precision of photovoltaic (PV) panels to the sun and the efficiency of solar energy utilization. Firstly, the hysteresis phenomenon in the servo motors of photovoltaic panels is considered, and the hysteresis-approximate inverse compensator is first studied in the servo motors of photovoltaic panels. Secondly, to deal with the constrained states such as rotor angle, angular velocity, and stator current in practical servo motors, and to ensure all states are strictly confined within each set of constraints with pre-set tracking performance, the asymmetric barrier Lyapunov functions and the error transformed functions are designed. Finally, to test the effectiveness of the proposed control strategy, a hardware-in-the-loop simulation platform and a photovoltaic servo system for PV power generation are built.

Motion planning and control strategy of a cable-driven body weight support gait training robot

Abstract. In this paper, a cable-driven body weight support gait training robot (C-BWSGTR) that provides patients with partial body weight support as well as a kind of stable gait training driving force was designed; this device enabled those patients to walk again. Firstly, the overall configuration of the C-BWSGTR was determined, and the structural composition and working principle of the robot were established. Secondly, the vector algebra method was applied to carry out the kinematic analysis and establish the mathematical model of the C-BWSGTR. The displacement of each cable during the patient gait training was also calculated. Thirdly, the motion planning of the C-BWSGTR was carried out in stages, using the time–phase distribution relationship based on an S-shaped speed curve. Meanwhile, the displacement, speed, and acceleration of each cable during the patient gait training were calculated and corresponding change curves were generated. Finally, a position servo composite control strategy for the C-BWSGTR was designed by analyzing the robot's dynamic characteristics of the forward channel transfer function. The simulation analysis and prototype experiment in this paper verified that the designed composite position servo control strategy can meet the requirements of the system with respect to stability and a fast response of the system to the loading command.

Pressure control for pneumatic pressing roller in automated fiber placement

In automated fiber placement (AFP), the contact pressure between the roller and the mold is an important process parameter. Too small or too large contact pressure will result in unacceptable laying defects. This paper focuses on the control method of contact pressure in AFP. Firstly, the dynamic model of the pressing foot mechanism is established, and a mathematical relationship of input air pressure and output force is developed. Then, a self-tuning PI control algorithm is used to implement servo control of the roller output force based on the Slowly Time-Varying Recursive Identification Algorithm. Also, using Abaqus/CAE, the mapping relationship between the contact area and measurements from displacement sensors is established to predict the contact area in real time. Finally, the contact pressure control method is established by combining the servo control method of contact force and the prediction method of contact area. Experimental results show that the constant pressure control method can effectively stabilize the contact pressure, with a pressure fluctuation of less than 4% under the experimental conditions set in this paper.

High precision tracking control for linear servo system based on intelligent second-order complementary sliding mode

High precision tracking control for linear servo system based on intelligent second-order complementary sliding mode

Hybrid vision/strain-based control strategy for a parallel manipulator with flexible links

Parallel manipulators may present higher speed/acceleration ratios and energy efficiency when compared with serial manipulators. In addition, reducing their components’ inertia can further improve performance. However, this design alternative might yield vibrations requiring novel joint and task space control strategies. While the former involves precise models, the latter might require adequate computation vision schemes. These requirements impose critical challenges. This manuscript proposes a hybrid control strategy and experimentally investigates using a 3RRR prototype with flexible links. This hybrid strategy comprises two control loops: position-based visual servo and strain-based feedback control schemes. The strain-based loop uses a sliding mode control and the time derivative of the signals obtained by strain gauges installed in the flexible links. Compared with the position-based visual servo scheme, the hybrid strategy can considerably attenuate the vibrations since the approach reduced the overshoot response by 36% and the maximum value of the Euclidean error on position by 38%, on average.

High-Performance Position Control for Repetitive Tasks of Motor-Driven Servo Systems Based on Periodic Disturbance Observer

Repetitive position control of the motor-driven servo system (MDSS) plays an important role in numerous industrial processing and production. In this article, based on the Euler–Lagrange equation, a dynamics model was established by analyzing the relationship of the energy conversion to describe the motion of an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$n$</tex-math></inline-formula> -degree-of-freedom MDSS. For repetitive position control tasks of the considered system, a robust controller was designed to improve the performance of the closed-loop system, where the disturbance observer was employed to approximate the periodic dynamics of the system to improve both the transient and steady-state performances. The stability of the closed-loop system was analyzed based on the Lyapunov method. Moreover, to validate the control effect of the proposed method, the coordinated contouring task was considered for a dual-linear-motor-driven gantry system, where a B-spline wavelet series was employed as the periodic disturbance observer. The results of the comparative experiment show not only the effectiveness of the designed control scheme but also the superiority of the B-spline wavelet series on the approximation of periodic functions.