Position Control Experiments Research Articles

Modeling and Control of a Road Wheel Actuation Module in Steer-by-Wire System

Since the steer-by-wire system removes the mechanical connection and uses electrical signals to drive the system, it has the disadvantage of being less stable in the failure of parts or systems. Therefore, in this paper, we present a methodology for developing a digital model of the road wheel actuator of the steer-by-wire system. First, the detailed dynamics of the road wheel actuator are analyzed and simplified, and the friction model is estimated and compensated to obtain the equilibrium inertia and damping coefficient of the motor and the road wheel actuator. And to verify the accuracy of the digital model developed based on these parameters, the outputs are compared by giving the same inputs under open-loop control. Furthermore, to solve the problem caused by nonlinear disturbance and model uncertainty, a disturbance observer-based position controller is proposed. The validity of the proposed controller and the validity of the digital model development methodology are confirmed by the results of the position control experiment.

Automatic mass balancing of spacecraft attitude simulators by optimal feedback control

There is an increasing interest in development of spacecraft attitude simulators. A necessary and challenging task in preparation for any attitude control experiment is to remove the gravitational disturbances on the simulator by a mass balancing system which relocates the center of mass to coincide with the center of rotation. This research is aimed at filling a substantial gap in the literature by presenting a methodical framework for analysis and design of closed-loop automatic mass balancing systems. In this regard, a state-space representation for imbalanced dynamics of attitude simulators is derived to enable the application of modern control techniques to the problem which will be shown to be very effective in achieving an accurate balancing. The model is further enhanced by state augmentation and incremental control input to address the practical requirements for an efficient balancing strategy. Next, an optimal feedback control is designed on the enhanced dynamics model to minimize the rotational kinetic energy and leveling accuracy as key performance measures of the problem. The simulation results and comparative evaluations with a previously validated method verified that the proposed modeling and control approach is effective in achieving an accurate mass balancing while providing a convenient and methodical analysis and design procedure.

PI Stabilizing Control of Nonaffine MIMO Systems by Additive-State-Decomposition Dynamic Inversion Design

This paper addresses the stabilizing control issue for a class of non-affine MIMO (Multiple Input Multiple Output) nonlinear systems subject to time-varying disturbance using an additive-state-decomposition dynamic inversion control scheme. First, the original system is transformed into a minimum phase system through a proposed output redefinition method. Then, the transformed minimum-phase system is further additively decomposed into a primary subsystem and a secondary subsystem. Next, the dynamic inversion control scheme solves the non-affine control problem. Stability analysis shows that the proposed control method guarantees all closed-loop system signals being semi-globally uniformly ultimately bounded. Finally, a simulation and an attitude control experiment of a quadcopter show the effectiveness of the proposed control method.

Emergence of a Euglena bioconvection spot controlled by non-uniform light

Microorganisms possess taxes, which are the behavioral response to stimuli. The interaction between taxis and fluid dynamic instability leads to a macroscopic flow called bioconvection. In this study, we demonstrated that an isolated, single, three-dimensional bioconvection cell can exist within Euglena suspension. The isolated convection cell was named a “bioconvection spot.” To reveal the formation of this bioconvection spot in a cylindrical container, position-control experiments were designed in a non-uniform light environment. Upon exposure of Euglena suspensions to varying light conditions with white and red regions, Euglena was determined to aggregate into the red (darker) region. This was attributed to its phototactic response of Euglena, causing its movement toward a darker environment and away from a strong light. Thus, the bioconvection spot was created by manipulating the local cell density of the suspension and the light environments. Using our experimental setup, we observed the structure of the spot and established that it radiated pulses of local cell densities of Euglena.

Small-Satellite Attitude Control Using Continuous Sinusoids With Strict Amplitude Constraints

This article considers attitude control of a rigid body (e.g., small satellite) with internal rotating-mass actuators that, unlike reaction wheels, cannot perform unrestricted rotations. Instead, the rotational stroke of each actuator is limited to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$[-\alpha,\alpha]$ </tex-math></inline-formula> rad, where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha &gt; 0$ </tex-math></inline-formula> . We present two attitude-feedback control methods. The first method addresses setpoint tracking of constant attitude commands, whereas the second approach addresses command following of time-varying attitude commands. Both methods use control signals that are continuous and piecewise sinusoidal but whose derivatives can contain discontinuities. The main analytic results show that these attitude-feedback controls achieve asymptotic setpoint tracking for a constant attitude command and approximate command following for a time-varying attitude command. The results also show that the controls satisfy the strict actuator amplitude constraint. Each control method is demonstrated in numerical simulations of a small satellite in deep space. Finally, we present single-axis closed-loop attitude control experiments for a small-satellite system on an air bearing.

Fault tolerant attitude control of under-actuated spacecraft: Theory and experiment

This paper investigates fault tolerant attitude control theory and experiment for under-actuated spacecraft with one reaction wheel completely broken and two others suffering actuator faults of partial loss of effectiveness or bias. A non-smooth robust adaptive fault tolerant control law is proposed under the zero-momentum and input saturation conditions. It shows that the available reaction wheels need to produce sufficient control torque for the fault tolerance. Such a new control method is implemented in a semi-physical simulation system of an air-bearing platform. Experimental results show the effectiveness of the proposed method in spacecraft practical engineering.

Attitude control experiment of a spinning spacecraft using only magnetic torquers

Magnetic torquers are attitude control devices used in spacecraft systems, and extensive research has been conducted on the attitude control of such spacecraft systems equipped with magnetic torquers. In this paper, a control law for spin spacecraft systems is proposed. Unlike existing control laws that switch between the spin rate and spin axis orientation control, the proposed angular momentum control law (AMCL) simultaneously provides feedback control for the spin rate and spin axis orientation based on the angular momentum error from the target. The steady-state and asymptotic behaviors of the angular momentum error are analyzed. In the analysis, both the saturated and unsaturated magnetic moments are considered. A testbed with magnetic torquers and a geomagnetic field simulator are developed to experimentally evaluate the performance of the AMCL. The geomagnetic field simulator is constructed using three Helmholtz coils to generate a time-variant magnetic field similar to that in orbit. The AMCL is used to conduct two ground experiments on the spin rate and spin axis orientation control. The effectiveness of the AMCL and behavior of the testbed are experimentally evaluated by comparing and analyzing the experimental and numerical simulation results. Consequently, the AMCL is found to achieve the required states in the experiments, and the asymptotic and steady-state behaviors appear to be consistent with the estimations made by numerical simulations. In conclusion, the proposed AMCL can appropriately control the spin motion of a spacecraft.

Disturbance rejection enhancement using predictive control for the fixed‐wing UAV with multiple ailerons

SummaryThe performance of small fixed‐wing unmanned aerial vehicles (UAVs) is easily degraded by exogenous disturbances. In an attempt to improve the performance, the structural change is made in conventional small fixed‐wing UAV through segmentation of each aileron control surface into multiples. Detailed system identification experiments are performed on each aileron pair in the wind tunnel to acquire linear dynamic models for the roll attitude of the UAV. These experiments have provided the transfer functions for the aileron control surfaces based on corresponding frequency response. Three distinctive model predictive controllers are designed and deployed in real‐time hardware to achieve the roll attitude control. The roll attitude control experiments are validated in wind tunnel under both normal and turbulent environments. The results show that multiple input and single output control system provides significant improvement in the roll attitude and disturbance rejection performance. The collective actuation of multiple control surfaces improves roll stability by to when compared to the single aileron pair based conventional control in the presence of turbulent flight conditions.

Sensor Fusion of Self-Sensed Measurements for Position Control of a Constant Air-Gap Solenoid

This article presents a novel constant air-gap solenoid (CAS) actuator design that can perform accurate and wide-bandwidth closed-loop position control with two fused self-sensed plunger measurements. The recently patented CAS actuator is experimentally validated to be the first electromagnetic actuator with the ability to simultaneously produce two plunger position measurements with complementary bandwidth characteristics. First, a variable reluctance differential solenoid transducer (VRDST) is converted into a stacked CAS actuator through minor geometry modifications. Next, two complementary self-sensing methods that are based on inductance and back electromotive force (BEMF) are selected. Then, a complementary filter design is proposed to fuse the inductance- and BEMF-based self-sensing methods. Afterward, the design and fabrication of the prototype CAS actuator and the experimental setup are discussed. The experimental setup is then used to characterize the prototype CAS actuator and observe the performance of the individual self-sensing methods. Finally, the fused measurement is used for feedback in closed-loop position control. The closed-loop position control experiments show that the self-sensed feedback performs comparably with a dedicated high-end laser vibrometer. Furthermore, the results show that the sensor fusion output performs better than the individual self-sensing methods.

Independent Control Strategy of Multiple Magnetic Flexible Millirobots for Position Control and Path Following

Magnetically actuated small-scale robots have great potential for numerous applications in remote, confined, or enclosed environments. Multiple small-scale robots enable cooperation and increase the operating efficiency. However, independent control of multiple magnetic small-scale robots is a great challenge, because the robots receive identical control inputs from the same external magnetic field. In this article, we propose a novel strategy of completely decoupled independent control of magnetically actuated flexible swimming millirobots. A flexible millirobot shows a crawling motion on a flat plane within an oscillating magnetic field. Millirobots with different magnetization directions have the same velocity response curve to the oscillating magnetic field but with a difference of phase. We designed and fabricated a group of up to four heterogeneous millirobots with identical geometries and different magnetization directions. According to their velocity response curves, an optimal direction of oscillating magnetic field is calculated to induce a desired velocity vector for the millirobot group, one of which is nonzero and the others are approximately zero. The strategy is verified by experiments of independent position control of up to four millirobots and independent path following control of up to three millirobots with small errors. We further expect that with this independent control strategy, the millirobots will be able to cooperate to finish complicated tasks.

Translational levitation of a permanent magnet above the splicing plane of superconducting blocks under zero field cooling and its motion drag

Benefited from the combination of Messiner effect and flux pinning, a permanent magnet (PM) can give the self-stable levitation above a bulk superconductor. The phenomenon provides the basic principle of superconductors in wide applications such as HTS maglev trains and superconducting flywheel systems. When the superconductor works under some conditions without the flux pinning (for example zero-field cooling), the PM will show free motion along multi freedoms due to the full diamagnetism of superconductor. This paper investigated the drag characteristics of the PM moved above the diamagnetic plane spliced by superconducting bulks. The spliced diamagnetic plane can get rid of the limitation of the size of the single superconducting bulk, and realize low-drag translational motion levitation in a large area. The article builds a multidimensional levitation force measurement device to measure the vertical force and lateral force of the PM translation when the superconducting plane works at different temperature. It is found that the lateral force distribution in the PM translation shows with alternating peaks and valleys. The increase of the suspending air gap can reduce the lateral force fluctuation and realize low-drag translation. The translational lateral force has the smaller value at the center of a single superconducting block, and can be measured at the level less than 1 mN. The low drag characteristics bring the potential application of superconducting translational levitation in the low gravity ground simulation for attitude and orbit control experiments of satellites.

Improved Integral Sliding Mode Control-Based Attitude Control Design and Experiment for High Maneuverable AUV

The Autonomous Underwater Vehicle’s body attitude has a great influence on some specific underwater tasks, such as topographic prospecting, target detection, etc. Therefore, this paper investigates an improved integral sliding mode control (IISMC)-based attitude controller for AUV with model uncertainties and external disturbances to improve the ability of attitude tracking for AUV. To reduce the influence of strong interference on the integral term, the Gaussian function is introduced in integral sliding mode controller. Moreover, the Lyapunov function is used to prove the stability of IISMC-based attitude control law. Finally, the numerical simulations on MATLAB/Simulink are provided to demonstrate the proposed IISMC has smaller tracking error and converges faster than Sliding Mode Control (SMC) and Integral Sliding Mode Control (ISMC)-based attitude-control laws under different disturbances. Better yet, the effectiveness of the proposed IISMC-based attitude control law is tested in field experiments.

Hybrid Antagonistic System With Coiled Shape Memory Alloy and Twisted and Coiled Polymer Actuator for Lightweight Robotic Arm

Artificial muscles have been developed for various input power sources. Among them, thermally driven actuators can be easily actuated at a low voltage without an additional device using the Joule heating. Therefore, these actuators can be considered suitable for developing lightweight robots. Shape memory alloy or twisted and coiled actuators are typically used as both have the advantage of large specific power; however, their disadvantages include speed, hysteresis, and initial tension. In this letter, we developed a hybrid antagonistic system that alleviates the drawbacks of both actuators. Control methods for hysteresis are applied based on actuator models and controlling the cooling fan. The joint position control experiment was conducted, and the advantages of the two actuators could be utilized based on the results. Furthermore, a lightweight robot arm was developed using the hybrid system. By applying the hybrid system, the robotic arm could be fabricated with a light weight of about 1 kg and can move in 4 degrees of freedom. The robotic arm was possible to perform angle control of the elbow with the developed control algorithm. In addition, it was combined with a 3 degrees of freedom orthogonal joint to replace the role of the shoulder, and the robotic arm was able to demonstrate the motion of activities of daily living.

Development of an extended proportional–integral–proportional control for improving positional motion performance of permanent magnet synchronous motor‐driven servomechanism

AbstractTo achieve high‐speed and high‐accuracy positional motions in a permanent magnet synchronous motor (PMSM)‐driven servomechanism, this study developed an extended proportional–integral–proportional (PIP) control, particularly by considering the limitations of the hardware structure of commercialized PMSM drivers. PIP feedback and feedforward controls were developed, such that the existing PIP feedback control, which is extensively used in commercialized PMSM drivers, can perform dynamic and friction torque compensations in PMSMs. Thereafter, an extended PIP control with the newly added design degrees of freedom was developed based on the PIP feedback and feedforward control structures, thereby further improving the position response of the PMSM‐driven servomechanism and positional motion performance of advanced motion control systems. Position control experiments were performed on a commercialized PMSM pack installed on the rotary table of a five‐axis computer numerical control (CNC) machining center. Results indicate that the extended PIP control can significantly reduce position errors, which can be minimally influenced by the change in frequency of the position command. Furthermore, circular motion experiments were performed along the motion axes of the five‐axis CNC machining center. Results indicate that the extended PIP control with dynamic matching design can significantly reduce the root‐mean‐square value of contouring errors and roundness error value. Experimental results validate the feasibility of the extended PIP control for improving the positional motion performance of the PMSM‐driven servomechanism.

Design of the high field side antenna of the new reflectometric system for plasma position estimate in RFXmod2

A reflectometric system will be installed in the RFX-mod2 experiment, consisting of 4 couples of transmitting/receiving antennas working in the range 16–26.5 GHz in X-mode wave propagation for tokamak discharges. They will be placed within dedicated plasma accesses in the same poloidal section at 4 equispaced poloidal positions, two on the equatorial plane, High Field Side (HFS)/Low Field Side (LFS), and two at the vertical top/bottom ports. This configuration was conceived to perform plasma position control experiments without using the magnetic measurement signals. While the accesses in LFS, top and bottom positions will accommodate pyramidal antennas, the strict room constraints in the HFS position required a special routing of the feeding waveguide and the design of a different type of antenna, described in the paper. The horn reflector (also named hoghorn) type was preferred which allows radiating (and receiving) a beam at a 90° direction with respect to the horn axis, which will be perpendicular to the equatorial plane. After fixing a reference working frequency f = 21 GHz (wavelength λ = 14.3 mm), an antenna fitting the available room was designed by means of the COMSOL Multiphysics Radio Frequency module. Four different versions were developed by introducing some modifications of the aperture shape to study their effect on the antenna performance. FEM analyses were run for frequencies in the 17–26 GHz interval to characterize the frequency response in terms of radiative patterns of the total and far electric field. The directivity of the antennae was also evaluated. The 4 versions exhibited comparable responses and the observed beam directional properties at the expected plasma distance were considered acceptable for the development of this application. A prototype of the antenna has been realized by additive manufacturing process.

Design of Position Control Method for Pump-Controlled Hydraulic Presses via Adaptive Integral Robust Control

This paper takes the position control performance of pump-controlled hydraulic presses as the research object. The control methods are designed respectively for the two motion stages of rapid descent and slow descent of hydraulic presses in order to improve the control performance of the system. First of all, the accuracy model of the pump-controlled hydraulic presses position servo system (the pump-controlled hydraulic presses position servo system, which is called PCHPS) and its MATLAB/Simulink simulation platform are established. Based on the theoretical analysis and experimental data, the interference factors affecting the tracking accuracy and positioning accuracy of the PCHPS are analyzed. Then, an adaptive integral robust control (the adaptive integral robust control, which is called AIRC) for PCHPS is designed to reduce the influence of nonlinear factors on the system, and the effectiveness of the controller is verified by simulation. Finally, the position control experiment of PCHPS is designed, and the experimental results show that the AIRC can effectively reduce nonlinear factors such as unknown interference in the slow-down stage of the system. The positioning accuracy is raised to within 0.008 mm, which improves the process level of the hydraulic presses.

The Operational Space Formulation on Humanoids Considering Joint Stiffness and Bandwidth Limit

As the applications of robots increase, mobility and capability of interaction in unstructured environments have become important. Hence, humanoid robots have been developed to have these capabilities, and recently, compliant motions for safe contact have been studied. The Operational Space Formulation can be an effective method for humanoid robots to realize compliant motion via unified motion and force control. Nevertheless, the implementation of the Operational Space Formulation on humanoid robots has not been successful. One of the challenging issues is low position tracking performance. In this study, a control method for solving this problem is proposed by considering the joint stiffness and joint bandwidth limits. To consider joint stiffness, the Operational Space Formulation was derived using flexible joint robot dynamics. Additionally, an extra torque generation method, which penalizes low performance actuators, is utilized to account for the bandwidth limits. Neither methods requires additional sensors or joint space controllers. Hence, they can be useful for conventional humanoid robots composed of electric motors and gears. By integrating the two methods, the position tracking performance of the Operational Space Formulation on the humanoid robot was significantly improved. The proposed method was demonstrated via position and orientation control experiments using our humanoid robot, TOCABI.

Experiments of position control for 3-link dual-arm underwater robot

Experiments of position control for 3-link dual-arm underwater robot

Motion Control and External Force Estimation of a Pneumatically Driven Multi-DOF Robotic Forceps

Robotic forceps with a rigid-link joint mechanism is orthodox for current robotic-assisted surgery systems. However, external force estimation without force sensors during operations is difficult for such electrically driven forceps. This work introduces a pneumatically driven multi-DOF (DOF: degree of freedom) forceps using a rigid-link mechanism with less interference of the wire drive between joints and realizes external force estimation by utilizing high back-drivability of pneumatic cylinders. We developed a position controller with dynamic compensation of the mechanical friction, in which the rotational angles of the three movable joints of the forceps are independently controlled. Moreover, we designed an external force observer in the position controller by applying the disturbance observer scheme. The results of the performance evaluation experiments are as follows. First, in the joint position control experiments, smooth and stable controllability is confirmed for sinusoidal reference inputs with the mean absolute errors of less than 2°. The resolution of the joint position control is approximately 1° for the response of step increasing reference inputs, which is acceptable for laparoscopic surgery. Second, the external force observer can correctly estimate the translational and the grasping forces with less than 20% errors of the maximum output forces. The practical sensitivities of the external force estimation are better than 0.5 N for translational forces and 0.2 N for grasping forces. The achieved performance of the developed forceps can be applicable for interactive force control in some particular surgical tasks such as suturing, ligation, organ traction and exclusion.

TWQH Attitude Control Experiments on Horizon Ground Simulator and Flight Test

This paper presents the results of two experiments on the Horizon ground simulator and outdoor flight test of TWQH hybrid UAV in presence of wind perturbation. The simulation results show the stability and error boundedness of the PID controller while the experimental inflight tests indicate the good performances of the proposed controller.