Actuator Position Research Articles

Simultaneous Positive and Negative Pressure Control Using Disturbance Observer Compensating Coupled Disturbance Dynamics

This letter introduces a simultaneous positive and negative pressure controller for a pneumatic pump. For precise position or force control of the pneumatic soft actuator, the pressure from the source has to be regulated. When the positive and negative pressures are regulated, coupled dynamics caused by the pressure change affect the controller performance. In other words, changes in the positive or negative pressure concurrently act as disturbances in the opposite pressure controller. Therefore, a disturbance observer is designed to compensate for the coupled pressure dynamics. A nominal model of the system is obtained based on the output-error model used in the MATLAB System Identification Toolbox. A simulation study is also performed to design a controller when the demand for the positive and negative pressures varies. Finally, a verification of the effectiveness of the controller is done through a series of experiments. In the step response test, the maximum pressure error of the positive and negative pressure was reduced from 0.159 to 0.152 kPa and from 0.3297 to 0.2334 kPa with the disturbance observer. Where positive and negative pressures change at the same time, the root mean square of the positive and negative pressure error decreased from 0.9701 to 0.4457 kPa and from 0.9848 to 0.4634 kPa applying the proposed pressure controller.

Design and Control of a Nonlinear Series Elastic Cable Actuator Based on the Hill Muscle Model

The bionic design of muscles is a research hotspot at present. Many researchers have designed bionic elastic actuators based on the Hill muscle model, and most of them include an active contraction element, passive contraction element and series elastic element, but they need more parametric design of mechanical structure and control under the guidance of Hill muscle model. In this research, a nonlinear series elastic cable actuating mechanism is designed in which the parameters of the elastic mechanism are optimized based on the Hill muscle model to fit the nonlinear passive elasticity of a muscle. Through the force–position relationship determined by the Hill muscle model, the output force and position of a nonlinear series elastic cable actuator are controlled to simulate the active contraction performance of a muscle. The experiments show that the proposed design and control method can make the nonlinear cable actuator have good muscle-like output force–displacement characteristics.

Development of a novel pneumatic positioning actuator equipped with new continuous air impulse generators

In this study, an innovative pneumatic positioning actuator is developed and tested. Furthermore, two novel mechanisms of crank-swinging lever and cam-follower that generate controlled air impulses are proposed, simulated in MSC.visualNastran software, and fabricated. The pneumatic actuator moves due to the recoil of an internally shot bullet. The bullet returns to its original place after one impact thanks to springs. The actuator and the base have a friction force that prevents hysteresis after each full forward movement. The recoil force is larger than the friction force, which causes the actuator to move. Meanwhile, since the spring force is smaller than the friction force, there is no movement during the return of the bullet. FLUENT and COMSOL software are employed to numerically study the proposed model and optimize the dimensions of the actuator. The problem consists of two components; solid mechanics and fluid-solid interface physics. The piston itself moves in a solid mechanic environment, and the air interaction and flow is related to laminar flow. Using the optimization part in Comsol, the parametric values of the proposed geometry are optimized. It is shown that the simulated device can provide repeatable displacements of 10 nm. The accuracy depends upon the magnitude of the air impact and the fabrication’s specifications and could decrease up to a few micrometers in each step. Repeating the steps gives a continuous stepped movement. Furthermore, the actuator moves in two directions using positive pressure or suction. The fabricated device can reach the positioning accuracy aimed in simulations.

The Design and Implementation of Control and Driving system with Double Position Feedback for Submarine Steering

With the well improvement of motor and power electronic technology, the technology of Electro-mechanical actuator (EMA)has come into a new stage. A high-reliability driving and controlling technology with a double redundancy feedback loop is described in this paper. In this method, the position of electromechanical actuator and the resolver position of motor can be back up for each other by some compensate algorithms. This method can improve the reliability of the control system without extra hardware and increasing cost.

Modeling and Position Control Simulation Research on Shape Memory Alloy Spring Actuator.

The shape memory alloy (SMA) actuator is widely used in aerospace, medical and robot fields because of its advantages of low driving voltage, large driving force, no noise and high-power–weight ratio. Therefore, it is of great significance to establish the theoretical model of the SMA actuator and analyze the driving characteristics of the SMA actuator. On the basis of summarizing the constitutive model of the shape memory alloy spring, the phase transformation dynamics model of SMA including the minor hysteresis loop is established using the Duhem model in this paper, and the theoretical models of the bias and differential SMA spring actuator are established. At the same time, a PID position controller including anti-saturation and anti-overheating functions is proposed to control the position of the SMA actuator. Finally, the position control simulation model of the SMA spring actuator is established and simulated. Simulation results show that the position of the SMA actuator can be well controlled by using the model and control method established in this paper.

Recursive Spectral Analysis-Based Diagnostic With Application to Electrohydraulic Actuators

This letter presents the diagnostic of electrohydraulic actuators. Different types of faults common in practice are considered such as a pump fault, abnormal viscous friction, oil contamination, and internal or external oil leakage. The entire diagnostic consists of two components: 1) reference tracking control; 2) recursive harmonic analysis. Firstly, the robust repetitive control is used such that the actuator position follows the harmonic reference signal. Secondly, the Fourier transforms of the control input at multiple harmonics are calculated recursively from sliding discrete Fourier transform. Instead of the raw control input, the modulated input signal is employed for better efficiency and robustness. The diagnostic decision is made based on distribution of the Fourier transforms. The effectiveness of the proposed method is demonstrated with numerical simulations. Diagnostic performance with different sizes of the sliding window is analyzed in terms of separation metrics, as a critical design parameter.

Parameter Estimation and Adaptive Control of Super-coiled Polymer Artificial Muscles

Super-coiled polymer (SCP) artificial muscles demonstrate desirable properties such as high-power density, compliance, and low-cost. However, their performance is dependent on the ambient environment. It is necessary but difficult to re-identify key SCP parameters to maintain desired performance. In this work, an adaptive parameter estimation method is proposed to identify unknown SCP parameters. The SCP model identification demonstrates parameter convergence which indicates that SCPs could be controlled effectively and used in environments with variations. We further develop a control law using direct model reference adaptive control (MRAC) on the output position of the SCP actuator. The MRAC performance is compared to a proportional-integral (PI) and proportional-derivative (PD) with feedforward controllers to demonstrate the ability to reduce tracking errors. The MRAC showed superior performance in comparison to the two controllers when the SCP actuator parameters were unknown.

A kinematic model of a humanoid lower limb exoskeleton with pneumatic actuators

Purpose: Although it is well-established that exoskeletons as robots attached to the human body’s extremities increase their strength, limited studies presented a computer and mathematical model of a human leg pneumatic exoskeleton based on anthropometric data. Methods: By using Inertial Measurement Units a lower limb joint angles (hip, knee and ankle in sagittal plane) during walking and running were calculated. The geometric model of a human leg pneumatic exoskeleton was presented. Joint angle data acquired during experiments were used in the mathematical model. Results: The position and velocity of exoskeleton actuators in each phase of the movement were calculated using the MATLAB package (Matlab_R2017b, The MathWorks Company, Novi, MI, USA). Conclusions: The obtained results demonstrate the efficiency of the proposed approach that can be utilized to analyze the kinematics of pneumatic exoskeletons using the dedicated design process. The developed mathematical model makes it possible to determine the position of lower limb segments and exoskeleton elements. The proposed model allows for calculating the position of the human leg and actuators’ characteristic points

Active Vibration Control of Railway Vehicle Car Body by Secondary Suspension Actuators and Piezoelectric Actuators

Active vibration suppression of high-speed electric multiple unit (EMU) car bodies was studied by the combined use of secondary suspension actuators and piezoelectric actuators. A vertical dynamics model was established considering secondary suspension actuators and piezoelectric actuators. The positions of the piezoelectric actuators and sensors were optimized using <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> norms. The feedback controller was designed using a robust optimal control method. The effects of the vibration devices and active control methods on the vehicle dynamic performance were simulated using MATLAB. The dynamic performance differences among the passive suspension vehicle, secondary vertical actuator installation vehicle, and active vibration control vehicle were compared and analyzed. The results show that the piezoelectric actuators and piezoelectric sensors were arranged at distances of 7.15, 12.25, and 17.35 meters from the left end of the car body, and the normalized <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> norms of the first and second order elastic modes of the car body were the largest, which can be used as piezoelectric actuators and sensor placement positions. Secondary suspension actuators can reduce rigid car body vibrations, and piezoelectric actuators can reduce elastic vibration. The higher the speed, the better is the acceleration suspension effect. When the vehicle speeds were 200 km∙h <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and 350 km∙h <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , the vehicle vibration acceleration decreased by 10% and 18%, respectively. Compared with the passive suspension system, the active vibration suspension system with a robust controller can reduce the rigid and elastic vibrations of the vehicle and improve ride comfort.

Failure prognosis and remaining useful life prediction of control moment gyroscopes onboard satellites

• A data-driven method for failure prognosis and RUL prediction of CMGs is proposed. • The proposed method reduces the need for historical data by 93.75%. • The proposed method uses General path model and Bayesian updating technique. • The proposed method has 96.25% accuracy when 30% of data is available for online prediction. Developing a Diagnosis, Prognosis, and Health Monitoring (DPHM) framework for a small satellite is a challenging task due to the limited availability of onboard health monitoring sensors and computational budget. This paper deals with the problem of developing a DPHM framework for a satellite attitude actuator system that uses single gimballed Control Moment Gyros (CMGs) in a pyramid configuration using only the attitude measurement data to eliminate the need for subsystem level sensor data acquisition. A data-driven model is used to mimic the nominal plant dynamics and fault is induced in the spin motor of the CMG of the satellite dynamics to generate run to failure data of the attitude control system. The general path model is applied to capture the prognosis of the system and using the parameters from the general path model as apriori information, the Bayesian updating technique is used to predict the remaining useful life of a system in real-time. The algorithm performs with 96.25% accuracy when 30% of data is available for online prediction.

Development of multi-input multi-output virtual tuned mass damper controls for the vibration suppression of structures

This study is concerned with the development of multi-input multi-output control algorithms for the active vibration suppression of structures using accelerometer signals and force-type actuators. The concept of the single-input single-output virtual tuned mass damper control algorithm developed in the previous study was extended to cope with multiple natural modes of structure equipped with a limited number of sensors and actuators. Two control algorithms were developed based on the assumption of collocated control. One is the decentralized virtual tuned mass damper control that produces the actuator signal using only the accelerometer signal of that actuator position. The other is the centralized virtual tuned mass damper control that is designed in modal-space, and produces the modal control force using the modal coordinate. Both the theoretical and experimental results show that the proposed control algorithms are effective in suppressing multiple natural modes with a lesser number of sensors and actuators. However, the decentralized virtual tuned mass damper control can be designed and implemented more easily than the centralized virtual tuned mass damper control.

Design of foldable PCBSat enabling three-axis attitude control

Satellite-on-a-printed circuit board (PCBSat) is a kind of femto-satellite that integrates all the electronic devices onto a PCB. Constrained by the energy/volume capacity, traditional attitude actuators no longer suit the PCBSat. In the paper, employing the flexible PCB material and micro-steppers, a new design that enables the PCBSat to fold and unfold is proposed, and a prototype is manufactured. The foldable PCBSat could achieve attitude maneuver by the spatial multibody dynamical effect. Meanwhile, the copper coils embedded in the boards can form a 3D magnetorquer when the PCBSat is at the orthogonal-fold status, making magnetic de-tumbling possible. Related theories combined with the detailed design of the PCBSat are introduced, and simulations are conducted to demonstrate the effectiveness of the attitude control mechanism.

Experimental study of position tracking control and pressure variation analysis on electrohydraulic system in open loop

This paper studies on the variable displacement electro-hydrostatic actuation system to control the position of hydraulic actuator with the used of bidirectional swashing variable displacement axial piston pump. The pump control system is more efficient than valve control system. The paper is focused on the experiment of position tracking of a symmetric linear hydraulic actuator in an open loop control, the demand of actuator is sinusoidal with frequencies of 0.10 to 0.25 Hz, amplitude of 0.1 m and offset of demand 0.1 m. The effective pressure force of the actuator depends on the chamber pressure variation of the actuator, the nature of pressure variation measured which played decisive role to control the position of the actuator. In industrial application, the role of the electrohydraulic system with accurate control is quite evident, the present experimental work emphasis to control the hydraulic actuator position.

Fractional Control of a Lightweight Single Link Flexible Robot Robust to Strain Gauge Sensor Disturbances and Payload Changes

In this paper, a method to control one degree of freedom lightweight flexible manipulators is investigated. These robots have a single low-frequency and high amplitude vibration mode. They hold actuators with high friction, and sensors which are often strain gauges with offset and high-frequency noise. These problems reduce the motion’s performance and the precision of the robot tip positioning. Moreover, since the carried payload changes in the different tasks, that vibration frequency also changes producing underdamped or even unstable time responses of the closed-loop control system. The actuator friction effect is removed by using a robust two degrees of freedom PID control system which feeds back the actuator position. This is called the inner loop. After, an outer loop is closed that removes the link vibrations and is designed based on the combination of the singular perturbation theory and the input-state linearization technique. A new controller is proposed for this outer loop that: (1) removes the strain gauge offset effects, (2) reduces the risk of saturating the actuator due to the high-frequency noise of strain gauges and (3) achieves high robustness to a change in the payload mass. This last feature prompted us to use a fractional-order PD controller. A procedure for tuning this controller is also proposed. Simulated and experimental results are presented that show that its performance overcomes those of PD controllers, which are the controllers usually employed in the input-state linearization of second-order systems.

A dimensionality reduction algorithm for mapping tokamak operational regimes using a variational autoencoder (VAE) neural network

A variational autoencoder (VAE) is a type of unsupervised neural network which is able to learn meaningful data representations in a reduced dimensional space. We present an application of VAE in identifying the operational stability boundary of tokamak plasma discharges. This model was implemented using a dataset of over 3000 discharges from the high beta tokamak-extended pulse (HBT-EP) device. We found the VAE model to be capable of forming a continuous low-dimensional operational space map and identifying the operational boundaries using a specified warning time window. By projecting the operational parameters onto the same reduced space, this provides an intuitive way for the machine operator or an automated control system to perform disruption avoidance using a relevant control actuator as a discharge approaches a boundary. Pre-programmed GPU control experiments were conducted to demonstrate this control technique using HBT-EP’s saddle control coils as a horizontal position actuator, showing the ability to avoid the oncoming disruptive event and extend the duration of the discharge.

Average Modeling and Nonlinear Observer Design for Pneumatic Actuators With On/Off Solenoid Valves

Abstract This paper presents a state-averaged model and the design of nonlinear observers for an on/off pneumatic actuator. The actuator is composed of two chambers and four on/off solenoid valves. The elaborated state-averaged model has the advantage of using only one continuous input instead of four binary inputs. Based on this new model, a high-gain observer and a sliding-mode observer are designed using the actuator position and the pressure measurements in one of the chambers. Finally, their closed-loop performance is verified and compared on an experimental benchmark.

Variable-gain control for continuum robots based on velocity sensitivity

Kinematic control for continuum robots usually involves an inverse model to provide actuator positions according to the desired end-tip position, as well as a servo controller at the actuator level. The resulting control performance of a continuum robot is then related to its kinematic characteristics that vary at different configurations. In this paper, a kinematic model for a typical rod-driven continuum robot is presented. Following this, a kinematic parameter, velocity sensitivity, is proposed to evaluate the kinematic characteristics of the continuum robot, indicating the contribution of the individual actuators to the instant movement of the end-tip when tracking a given path. Next, a variable gain control strategy is presented to tune the servo controller with respect to the varying velocity sensitivity along the path, reducing the fluctuation of the tracking errors in real time. The simulated and experimental results show that the presented methods can effectively smooth the movement of the continuum robot over its workspace by considering the coordination between the kinematic and servo controllers.

Research of active vibration control optimal disposition based on CMQPSO

The adaptive quantum particle swarm optimization algorithm based on cloud model and the multi-island genetic algorithm [15] have obvious advantages in convergence speed to solve the sensor optimization problem, and can effectively achieve global optimization. Due to the installation of sensors and actuators, the electromechanical coupling coefficient of intelligent structures is changed, which affects the vibration energy of structures. In this paper, the reserved energy index of structural vibration control system is taken as the objective optimization function. The position, number, length and control gain of sensors and actuators of active vibration control system are optimized. The adaptive Quantum-behaved Particle Swarm Optimization algorithm in cloud model(CMQPSO) is used as the optimization strategy, and the cantilever beam is taken as an example. This approach is verified its effectiveness and feasibility. It is found that excellent optimization results are obtained.

Application of Fuzzy Neural Network PID In Laser-guided Mortar Projectile

Based on the high control performance requirement of laser-guided mortar control system, the permanent magnet synchronous motor (PMSM) is adopted in this paper as the electromechanical actuator of the system, the mathematical model of the motor is analyzed, and the vector control technology is adopted to achieve precise control of position, speed and torque of the electromechanical actuator. Aiming at the characteristics of non-linearity, strong coupling and large parameter changes of the system in flight, an improved fuzzy neural network PID control method is proposed by combining the classical PID control algorithm with fuzzy control and neural network control algorithm to realize the real-time tuning and optimization of PID parameters. The mathematical model of the electromechanical actuator control system is established and simulated. The results show that the fuzzy neural network PID control has good tracking performance, small amplitude error, and strong adaptability to load changes.

Application of synthetic jet arrays for flow separation control on a circular “hump” model

This research investigates the effectiveness of a spanwise array of synthetic jet actuator (SJA) for the control of boundary layer separation over a circular “hump” model. The influence of geometrical and operational parameters – including actuator position, velocity ratio (i.e., the ratio of the peak exit jet velocity of actuators to the freestream velocity of cross flow, VR) and the actuation waveform – on the flow separation control are investigated using hot-wire anemometry (HWA) and particle image velocimetry (PIV) techniques. The effect of the position of SJA array on flow separation control has been studied experimentally over a considerable length of the hump chord (from the “apex” of the model to near the “trailing edge”) for the first time. The investigation looks in more detail into the mechanisms behind the alleviation of adverse pressure gradient as a key factor controlling the flow separation. The investigation of the effect of VR on the performance of SJAs shows the importance of the momentum injection in the mitigation of the momentum deficiency as another important factor in turbulent boundary layer flow separation. A holistic overview of the control parameters allowed to reveal a considerable change in the separation flow patterns. The results show that the best performance of SJA array from the viewpoint of separation control occurs at the velocity ratio of 1.85 with a reduction of the length of recirculation region of around 42.6 and 44.2% by using sine and square waves excitation of SJAs, respectively.