Accurate Position Control Research Articles

Aluminum Eddy Currents in PSRM Stator Arrays: Analysis and Mitigation for Improved Control Precision and Energy Efficiency

In this article, the influence of aluminum eddy currents in the PSRM stator array on electromagnetic properties and control performance is investigated. A model is developed to analyze the eddy current density distribution based on Maxwell’s equations, and an inductance model is derived that considers the eddy current effect. The effect of aluminum eddy currents on PSRM position control performance is qualitatively analyzed. The distribution of aluminum eddy currents and ohmic loss is verified through finite element analysis. The validity of the developed inductance model is experimentally verified. A material substitution method is proposed to eliminate the aluminum eddy current. Experimental results show that the position control accuracy of the PSRM prototype is improved by an average of 6.94% after the elimination of aluminum eddy currents, while the motor efficiency is improved by 6.51%.

An Overview of Flexible Jointed Robots

Background: Since the first industrial robots were created in the middle of the last century, robotics has shown strong growth prospects. Robotics has developed rapidly over time and is being used in more and more areas. Because of the need to minimize impact forces during robot movement, traditional rigid robots are no longer sufficient, flexible joints are more adaptable to the environment due to their adjustable stiffness and have higher application value in humancomputer interaction. Therefore, flexible jointed robots have become one of the research hotspots in recent years. Objective: Through a detailed analysis of the existing hardware and software control technologies of flexible joint robots, referring to papers and recent patents on flexible jointed robots, we aim to find ways to reduce the impact of flexible joint deformation of flexible joint robots and improve the overall force and position control accuracy of flexible joint robots. Methods: To categorize the hardware and software technologies of flexible jointed robots, to briefly explain the directions of the technologies categorized and to study them, to summarize the advantages and disadvantages of each type of technology respectively, and to outlook the future development trend. Results: Through the study and analysis of the various parts of the flexible joint robot, it can be seen that joint flexibility is mainly achieved through the drive motor and flexible components to achieve flexibility and then through the fusion control technology to control the deformation of the joint. Differences in structural materials affect the mechanical properties of robot motion. The detection and feedback accuracy of the sensor also has a significant impact on the control accuracy. Conclusion: The use of new motor technology, flexible component technology, material technology, and sensor technology, combined with improvements in software fusion control technology can reduce the impact of joint deformation, improve the control accuracy of joint flexibility, and achieve high-precision force-level control capability of flexible joint robots.

DESIGN OF BLDC MOTOR BASED POSITION CONTROL DRIVE

The objective of this work is to analyse an accurate position control of the BLDC motor using Field Oriented Control (FOC) algorithm. The BLDC motor, owing to its operational principle, boasts faster responses and higher torque, along with reduced noise, fewer spark-related issues, and lower maintenance requirements than classical DC motors. Field-Oriented Control (FOC) is an advanced control algorithm initially developed and utilized for induction and synchronous motor drives. By implementing a suitable coordinate system transformation, it becomes feasible to autonomously regulate the machine's flux and torque, akin to controlling a DC motor. To control its position accurately, you need to manipulate the stator currents and voltages. The FOC, also known as vector control, is a sophisticated control algorithm used to control BLDC motors. Field- Oriented Control (FOC) allows for the individualistic control of torque and flux. It offers a rapid dynamic response, exceeding the demands of applications such as washing machines. FOC eliminates torque ripple and enables precise motor control, delivering smooth and accurate performance across a wide range of speeds. In this project we use the FOC algorithm to identify the position control of BLDC motor. FOC delivers superior dynamic response in contrast to traditional control techniques. After performing the circuit in MATLAB and stimulating the circuit Analyze a waveform/ output. Before implementing the control system in a real BLDC motor, it is essential to simulate and test it thoroughly. Tools like MATLAB/Simulink are often used for simulation. KEYWORDS: BLDC; FOC; Hall effect sensor; Motor; Position

Performance of Position, Force, and Impedance Controllers for a Pneumatic Cylinder Ankle Exoskeleton

Abstract The best exoskeleton control strategy depends on the task, motivating the development and analysis of an exoskeleton capable of position, force, and impedance control. In this paper, we implement and compare the three controller types via sliding mode control on a custom-built pneumatic cylinder ankle exoskeleton. To evaluate each controller's performance, the exoskeleton was tested on the benchtop and with human subject experiments. With the position controller, the exoskeleton achieved an root-mean-square error (RMSE) of under 5 deg for both the benchtop and human tests. It had a bandwidth of approximately 12 rad/s. The force controller tracked sinusoidal trajectories acceptably well at low frequencies (15% of force range at 6 rad/s), with a bandwidth of approximately 24 rad/s. The error was significantly higher (RMSE of 24% of force range) for the more biologically relevant trajectory. The impedance controller demonstrated the desired spring-like behavior, with position RMSE generally under 5 deg compared to expected position. All three controllers worked equally well for benchtop and human tests. Thus, a pneumatically powered ankle exoskeleton with sliding mode control is capable of accurate position and impedance control and is capable of marginally acceptable force control.

Sensorless control of a PMSM based on an RBF neural network-optimized ADRC and SGHCKF-STF algorithm

For the problem of the rotor position estimation and control accuracy of permanent magnet synchronous motor (PMSM), this paper proposes a PMSM sensorless based on radial basis function (RBF) neural network optimized Automatic disturbance rejection control (RBF-ADRC) and strong tracking filter (STF) improved square root generalized fifth-order cubature Kalman filter (SGHCKF-STF). The Automatic disturbance rejection control (ADRC) has strong robustness, but there are many parameters and difficult to adjust. Now we use RBF neural network to adjust the parameters in ADRC online so as to improve the robustness and anti-disturbance ability. In order to improve the estimation accuracy of rotor position and speed, the orthogonal triangle (QR) decomposition and STF are introduced on the basis of the generalized fifth-order cubature Kalman filter (GHCKF) to design the SGHCKF-STF algorithm that not only ensure the non-positive nature of the covariance matrix but also improve the ability to cope with sudden changes in state during the filtering process. Experimental results show that the combination of RBF-ADRC and SGHCKF-STF improve the sensorless control effect of the PMSM to some extent.

Modeling and analysis of the influence caused by micro-vibration on satellite attitude control system

A closed-loop integrated model including micro-vibration disturbance, dynamic characteristics of satellite, optical system of star sensor and attitude control algorithm is established. The control torque error caused by additional disturbance torque and the star sensor imaging error caused by structural resonance is fully integrated analyzed, which are firstly presented into the attitude control system (ACS). Steady-state and transient response analyses are completed to evaluate the impact of such two errors on performances of (ACS). Steady-state response results show that the effect of control torque error appears in lower frequency band with a peak of 6.784E-8″ at 53 Hz, while influence of star sensor imaging error on attitude determination mainly concentrates in high frequency band with maximum response of 0.4101″ at 315 Hz. Transient response results show that the two errors will not significantly affect control indicators such as rise time, overshoot and peak time. The results indicate that the influence of star sensor imaging error is non-negligible for satellite ACS which required milli-arc-second attitude control accuracy. According to the analytical results, traditional analysis only on payload optical axis cannot reveal the whole impact of micro vibration on LOS error, the two errors of micro-vibration introduced to ACS in this work must be considered for the development of spacecraft with 0.1″ pointing accuracy.

Adaptive Position Control Strategy of SRM-Based EMA System for Precision Position Tracking

The electromechanical actuator (EMA) driven by switched reluctance motor (SRM) is promising to be used in the steering vane control system on the landing craft air cushion (LCAC) hovercraft due to its reduced maintenance costs and increased control flexibility. However, the system parameter uncertainty, the unknown load disturbance, and the large torque ripple of SRM make it challenging to achieve high position control precision. To improve the position control accuracy of the SRM-based EMA system, an adaptive position control strategy is proposed in this paper. Firstly, an adaptive fast terminal sliding mode controller (AFTSMC) is designed to address the issues of model parameter estimation and load disturbance rejection, which improves the dynamic response performance of the SRM-based EMA system. Secondly, a current-limited direct torque controller (CL-DTC) is proposed to track the reference torque calculated by AFTSMC with lower torque ripple and to limit the excessive currents of SRM at the same time, which helps further enhance the position control precision and prevent the SRM-based EMA from overheating. Finally, the proposed position control strategy is tested and compared with other three position controllers based on simulations and experiments. The results demonstrate the effectiveness and superiority of the proposed position control strategy.

Model prediction controller for penetration mechanism of seabed cone penetration test system

The system of seabed Cone Penetration Test (CPT) is a kind of equipment for offshore investigations. Seabed CPT is used to assess multiple physical properties of marine sediments. Constant-rate penetration mechanism is the core part of seabed CPT, which adopts dual-cylinder drive to penetrate the probe rod into the seafloor sediments at a constant speed (2cm/s). At present, the domestic CPT and its penetration equipment almost all rely on imports. In the process of system design, we found that the traditional PID control of the hydraulic cylinder position control accuracy is low, so we need to study higher precision position tracking control method to achieve uniform penetration of the probe rod. In this paper, a Linear Time-Varying Model Predictive Controller (LTV-MPC) is introduced, which can control two hydraulic cylinders to penetrate probe rod into the seabed sediment with smaller penetration rate error under the condition of changing penetration resistance.

Optimized Sliding Mode Control Based on Cuckoo Search Algorithm: Application for 2DF Robot Manipulator

Robot manipulators are used in high-accuracy processes they provide flexibility, adaptability, and a large workspace. Hence, in the presence of uncertainties, disturbance, and high-performance control approaches are necessary to improve their accuracy to achieve high-tracking precision requirements and transient response under load variation. We present in this article, a novel concept of robust nonsingular fast terminal sliding mode controller (NFTSMC). In fact, the use of the NFTSMC offers a fast convergence rate, avoids singularities but still suffers from chattering. To overcome this limitation, two approaches have been developed: robust nonsingular fast terminal sliding mode controller (RNFTSMC) and robust optimized nonsingular fast terminal sliding controller (RONFTSMC). In the first one an additional term called switching signal is added to the equivalent control law. The second one is a combination of the NFTSM technique, and a cuckoo search algorithm as optimum term. Simulations show that the control strategy can overcome the chattering phenomena ensures the accuracy and stability of the joint robot position control.

Task space control of ram poses of multipoint Servo Presses

Robotic manipulators are known for their numerous degrees of freedom with which they can manipulate objects in task space. With the help of model-based control concepts, it is possible to precisely closed-loop control their pose, thus meeting high positioning accuracy requirements. As a result, they are ideally suited for carrying out flexible activities in manufacturing processes in which freely programmable tool paths are required, such as pick and place, welding or assembly tasks. If high forces have to be applied in manufacturing processes, as is the case in bulk forming processes, robots can no longer be used due to low stiffness and moderate force provision. The development of flexible forming machines with several degrees of freedom overcomes this problem. Machine tools such as the 3D Servo Press have three ram degrees of freedom and can provide forces of up to 1600 kN, but require highly accurate position control in task space. For this reason, this paper shows how control concepts from robotics can be applied to machine tools with high stiffness, high provided forces and multiple degrees of freedom. The functionality of the control is validated using the example of upsetting tests in which off-center forces are applied to the ram and the control counteracts tilting of the ram.

Research on Positioning Control Strategy for a Hydraulic Support Pushing System Based on Iterative Learning

At present, the positioning control of the hydraulic support pushing systems in fully mechanized mining faces uses an electrohydraulic directional valve as the control component, while the current research mainly focuses on servo valves, proportional valves, high−speed on−off valves, and electromagnetic directional valves. At present, the positioning control for electrohydraulic directional valves is only a simple logical control. Therefore, in order to improve the positioning control accuracy of the hydraulic support pushing system, a predictive positioning control strategy based on iterative learning was designed. Firstly, mathematical modeling of the hydraulic support pulling process was carried out, and its state−space equation was established. Secondly, an iterative learning controller with a state observer was designed, in which the iterative learning method was used to predict the control advance in the positioning process, and the state observer was used to estimate the parameters that could not be measured by the system, so as to improve the control accuracy in the broaching process. Then, a SimulationX–Simulink joint simulation model of the position control system of a multi−cylinder pulling hydraulic support was built, and the designed iterative learning controller was compared with the BP neural network controller. Finally, a test platform for the hydraulic support pushing system was built, and the proposed control strategy was experimentally verified. The research results show that the iterative learning control strategy proposed for the electrohydraulic directional valve not only simplifies the design process of the controller but also has higher positioning control accuracy. The single−cylinder positioning control accuracy can be controlled within 10 mm, and the multi−cylinder coordinated positioning control accuracy can be controlled within 15 mm, which meets the accuracy requirements of the site.

Linear actuator using heat-responding artificial muscle

Artificial muscles have a linear motion that mimics the bio muscle in response to electric stimuli.it can be made of different types like IPMC, pneumatics, sliding model, and hyper-twisted polymer. Linear actuators the actuators that possess linear motion are highly important in industry 4.0 as blooming tech raises. We focus on the construction of linear actuators for heavy-weight applications with accurate position control and PWM response movement. Current linear actuators used in industries and systems are mainly comprised of electric motors, and a huge loss of energy occurs while the transfer of rotational to linear motion.

Sliding Mode Control with Feedforward Compensation for a Soft Manipulator That Considers Environment Contact Constraints

Soft manipulators have desirable environmental compatibility because of their pliability. However, this pliability also brings challenges to modeling and control when considering contact or collision with the environment. In previous work, we established several mathematical models for describing fluidic soft manipulators under environmental effects and verified their accuracy. However, the controller design for a soft manipulator is still a significant challenge, especially under the conditions of environmental contact. In this paper, we build upon our previously established work by conducting feedforward compensation for a soft manipulator under contact constraints and designing a sliding mode controller based on an operational space dynamics model. Then, we combine the feedforward compensation model with the sliding mode controller to realize accurate position control of the soft manipulator. Finally, simulation and experimental results show that this controller can accurately and effectively control the position of the soft manipulator.

Integrated Position and Speed Control for Rail Transit Doors Based on Speed-Current Loop

Different from typical servo systems that take position control as the first priority, rail transit door needs to reach the specified position with the established speed curve, so as to meet the safety requirements. Hence, both speed control and position control are simultaneously required, which cannot be achieved by the conventional cascaded position-speed-current loop structure. In this paper, an integrated position and speed control method for rail transit door based on speed-current loop structure is proposed. The movement of the door is divided into four stages, in which the speed mode or position mode are applied according to the instantaneous position of the door. In the last stage of position servo, in order to improve the accuracy of position control at low speed and meet the safety requirements, a method based on chopper regulator is proposed to realize servo accuracy and accident protection by adjusting the chopper current limit. Simulation and experimental results show that the proposed method is effective and easy to implement in engineering practice.

A head template for computational dose modelling for transcranial focused ultrasound stimulation

Transcranial focused Ultrasound Stimulation (TUS) at low intensities is emerging as a novel non-invasive brain stimulation method with higher spatial resolution than established transcranial stimulation methods and the ability to selectively stimulate also deep brain areas. Accurate control of the focus position and strength of the TUS acoustic waves is important to enable a beneficial use of the high spatial resolution and to ensure safety. As the human skull causes strong attenuation and distortion of the waves, simulations of the transmitted waves are needed to accurately determine the TUS dose distribution inside the cranial cavity. The simulations require information of the skull morphology and its acoustic properties. Ideally, they are informed by computed tomography (CT) images of the individual head. However, suited individual imaging data is often not readily available. For this reason, we here introduce and validate a head template that can be used to estimate the average effects of the skull on the TUS acoustic wave in the population.The template was created from CT images of the heads of 29 individuals of different ages (between 20–50 years), gender and ethnicity using an iterative non-linear co-registration procedure. For validation, we compared acoustic and thermal simulations based on the template to the average of the simulation results of all 29 individual datasets. Acoustic simulations were performed for a model of a focused transducer driven at 500 kHz, placed at 24 standardized positions by means of the EEG 10–10 system. Additional simulations at 250 kHz and 750 kHz at 16 of the positions were used for further confirmation. The amount of ultrasound-induced heating at 500 kHz was estimated for the same 16 transducer positions. Our results show that the template represents the median of the acoustic pressure and temperature maps from the individuals reasonably well in most cases. This underpins the usefulness of the template for the planning and optimization of TUS interventions in studies of healthy young adults. Our results further indicate that the amount of variability between the individual simulation results depends on the position. Specifically, the simulated ultrasound-induced heating inside the skull exhibited strong interindividual variability for three posterior positions close to the midline, caused by a high variability of the local skull shape and composition. This should be taken into account when interpreting simulation results based on the template.

Design of Two-Degree-of-Freedom Fractional-Order Internal Model Control Algorithm for Pneumatic Control Valves

In response to the problems of the inaccurate pneumatic control valve model, the slow valve position control, and the low precision in the industrial control process, some improvement methods are proposed. Firstly, the fractional-order concept is introduced based on the first-order inertia model and IBBO (improved biogeography-based optimization) is used for iteration to obtain a specific transfer function model. Secondly, a fractional-order and two-degree-of-freedom combined internal model control algorithm is proposed. Finally, semi-physical experiments are carried out on a semi-physical experimental platform. The results show that in the field of pneumatic regulating valves, the fractional-order model has good adaptability and effectiveness, and the two-degree-of-freedom fractional-order internal model control algorithm also effectively improves the accuracy, speed, and robustness of the valve position control.

Optimal force control of a permanent magnet linear synchronous motor with multiple shuttles

Using permanent magnet linear synchronous machines for transportation tasks offers a higher flexibility in production plants compared to conventional conveyor solutions. In this context, passive transportation devices (shuttles) with permanent magnets are commonly used. When multiple shuttles are operated in close vicinity, disturbances due to magnetic interaction can occur. To allow for high-speed operation of the motor with high position control accuracy, these coupling effects must be considered. This paper presents a model-based control strategy that is based on a magnetic equivalent circuit model which is able to describe the nonlinear magnetic behavior at low computational costs. A framework is derived for the model calibration based on measurements. An optimal control scheme for the multi-shuttle operation is derived that allows to accurately track the desired tractive forces of the shuttles while minimizing the ohmic losses at the same time. The control concept is experimentally validated on a test bench and compared to a state-of-the-art field-oriented control concept typically used in industry.

Research on a Three-Dimensional Fuzzy Active Disturbance Rejection Controller for the Mechanical Arm of an Iron Roughneck

In the position control of the mechanical arm of an iron roughneck (MAIR), a controller with high responsiveness, high accuracy, and high anti-interference capability is necessary. An MAIR consists of two proportional-valve-controlled single-extension (PVCSE) hydraulic cylinders, and a traditional proportional–integral–derivative (PID) controller cannot easily achieve the accuracy and robustness requirements of the hydraulic cylinders. In this paper, a three-dimensional fuzzy active disturbance rejection controller (TF-ADRC) is proposed for an MAIR, which adds a three-dimensional fuzzy module to a classical active disturbance rejection controller (ADRC) to adjust the controller output according to the tracking of differential deviation, deviation change rate, and deviation change acceleration rate. Firstly, the trajectory planning of the MAIR was carried out using the quintic polynomial interpolation method to improve the smoothness of the target trajectory. Then, the reliability of the established model was verified by experiments. Finally, the comprehensive performance of a PID controller, fuzzy PID controller, ADRC, and TF-ADRC were compared based on the AMESim-Simulink model. The system with the TF-ADRC exhibits higher position control accuracy and better anti-interference capability than the system with a PID or Fuzzy PID controller, and accuracy is higher compared with the common ADRC.

Spacecraft Attitude Measurement and Control Integration Using a Novel Configuration of Variable Speed Magnetically Suspended Control and Sensing Gyroscope

For the sake of achieving the high-accuracy and high-bandwidth attitude measurement and control integration of flexible spacecraft, an integrated method based on a novel configuration of Variable Speed Magnetically Suspended Control and Sensitive Gyroscope (VSMSCSG) and Radial Basis Function (RBF) neural network control is proposed in this paper. First, the structure and principle of a novel VSMSCSG configuration are given, and its modelling is established. VSMSCSGs are employed as both actuators and attitude-rate sensors. Second, the attitude measurement method based on the configuration is proposed in the case of rotor spin speed and deflection angle changing. Based on the characteristics of the novel configuration, the corresponding RBF neural network attitude control law of spacecraft and the adaptive saturation avoidance steering laws of the VSMSCSGs have been further designed; the rotor can deflect at high frequency and change speed simultaneously to output a high bandwidth attitude control moment which dramatically improves the moment output capability of VSMSCSG configuration. Compared with the traditional method of attitude measurement and control integration, the proposed one not only improves the speed and accuracy of attitude control under high bandwidth disturbance but also greatly improves the accuracy of attitude measurement by fully using the dynamic information of novel configuration. Semiphysical simulation results demonstrate the correctness and superiority of the proposed method.

Cylinder position control driven by pneumatic digital bridge circuit using a fuzzy algorithm under large stroke and varying load conditions

A digital bridge circuit based on the concept of independent metering control can enable the precise position control of a pneumatic cylinder, but large strokes and variable loads still cause challenges. To solve this problem, a piecewise on/off valve flow compensator and a composite friction observer were innovatively designed in this study, and they were combined with a multiple fuzzy intelligent algorithm to ensure the accuracy and robustness of pneumatic position control. Considering the starting and stopping delays and the response processes of on/off valves, a six-stage flow–duty ratio linearization relationship was proposed. Employing a parameter identification method, a static and dynamic composite friction model was presented. Then, a fuzzy PID controller was proposed, and a genetic algorithm was used to optimize the control parameters. Experiment results showed that, when focusing on a large stroke (250 mm) and varying loads (8.5–18.5 kg), for sinusoidal signal with amplitude of 150 mm and frequency of 0.125 Hz and the air supply pressure is 0.5 Mpa, the algorithm in this study could ensure that the steady-state step response error was less than 1% and the root mean squared error of the sinusoidal trajectory tracking was less than 3%.