Inverse Dynamics Compensation Research Articles

A novel control strategy for reproducing the floor motions of high-rise buildings by earthquake-simulating shake tables

To enable the experimental assessment of the seismic performance of full-scale nonstructural elements with multiple engineering parameters (EDPs), a three-layer testbed named Nonstructural Element Simulator on Shake Table (NEST) has been developed. The testbed consists of three consecutive floors of steel structure. The bottom two floors provide a space to accommodate a full-scale room. To fully explore the flexibility of NEST, we propose a novel control strategy to generate the required shake table input time histories for the testbed to track the target floor motions of the buildings of interest with high accuracy. The control strategy contains two parts: an inverse dynamic compensation via simulation of feedback control systems (IDCS) algorithm and an offline iteration procedure based on a refined nonlinear numerical model of the testbed. The key aspects of the control strategy were introduced in this paper. Experimental tests were conducted to simulate the seismic responses of a full-scale office room on the 21st floor of a 42-story high-rise building. The test results show that the proposed control strategy can reproduce the target floor motions of the building of interest with less than 20% errors within the specified frequency range.

A Comparative Study between NMPC and Baseline Feedback Controllers for UAV Trajectory Tracking

Transport, rescue, search, surveillance, and disaster relief tasks are some applications that can be developed with unmanned aerial vehicles (UAVs), where accurate trajectory tracking is a crucial property to operate in a cluttered environment or under uncertainties. However, this is challenging due to high nonlinear dynamics, system constraints, and uncertainties presented in cluttered environments. Hence, uncertainties in the form of unmodeled dynamics, aerodynamic effects, and external disturbances such as wind can produce unstable feedback control schemes, introducing significant positional tracking errors. This work presents a detailed comparative study between controllers such as nonlinear model predictive control (NMPC) and non-predictive baseline feedback controllers, with particular attention to tracking accuracy and computational efficiency. The development of the non-predictive feedback controller schemes was divided into inverse differential kinematics and inverse dynamic compensation of the aerial vehicle. The design of the two controllers uses the mathematical model of UAV and nonlinear control theory, guaranteeing a low computational cost and an asymptotically stable algorithm. The NMPC formulation was developed considering system constraints, where the simplified dynamic model was included; additionally, the boundaries in control actions and a candidate Lyapunov function guarantees the stability of the control structure. Finally, this work uses the commercial simulator DJI brand and DJI Matrice 100 UAV in real-world experiments, where the NMPC shows a reduction in tracking error, indicating the advantages of this formulation.

Stable Bilateral Teleoperation Control Method for Biped Robots with Time-Varying Delays

This document proposes a control scheme applied to delayed bilateral teleoperation of the forward and turn speed of a biped robot against asymmetric and time-varying delays. This biped robot is modeled as a hybrid dynamic system because it behaves as a continuous system when the leg moves forward and discrete when the foot touches the ground generating an impulsive response. It is proposed to vary online the damping according to the time delay present in the communication channel, and the walking cycle time using an optimization criterion, to decrease the teleoperation system errors. To accomplish this, a three-phase cascade calibration process is used, and their benefits are evidenced in a comparative simulation study. The first phase is an offline calibration of the inverse dynamic compensation and also the parameters of the bilateral controller. The second phase guarantees the bilateral coordination of the delayed teleoperation system, using the Lyapunov–Krasovskii stability theory, by changing the leader damping and the equivalent follower damping together. The third phase assures a stable walk of the hybrid dynamics by controlling the walking cycle time and the real damping to move the eigenvalues of the Poincaré map, numerically computed, to stable limit cycles and link this result with an equivalent continuous system to join both phases. Additionally, a fictitious force was implemented to detect and avoid possible collisions with obstacles. Finally, an intercontinental teleoperation experiment of an NAO robot via the Internet including force and visual feedback is shown.

Inductor Saturation Compensation in Three-Phase Three-Wire Voltage-Source Converters Via Inverse System Dynamics

In three-phase three-wire (3P3W) voltage-source converter (VSC) systems, utilization of filter inductors with deep saturation characteristics is often advantageous due to the improved size, cost, and efficiency. However, with the use of conventional synchronous frame current control methods, the inductor saturation results in significant dynamic performance loss and poor steady-state current waveform quality. This article proposes an inverse dynamic model-based compensation (IDMBC) method to overcome these performance issues. For this purpose, two-phase exact modeling of the 3P3W VSC control system is obtained. Based on the modeling, the inverse system dynamic model of the nonlinear system is obtained and employed such that the nonlinear plant is converted to a virtual linear inductor system for linear current regulators to perform satisfactorily. Further, to control phase currents in the synchronous frame, a two-phase coordinate transformation is proposed. The IDMBC method is tested via dynamic command response and waveform quality simulations and experiments that employ saturable inductors reaching down from full inductance at zero current to 1/9th inductance at full current. The results obtained demonstrate the suitability of the method for 3P3W VSCs employing saturable inductors.

Study on control method for actuator of tire-suspension HILS system

In recent years, model-based development such as the HILS system has been used to save time and cost in the development of complex systems such as automobiles. Tire-suspension HILS system was a hybrid method with vehicle dynamics analysis and bench test of the tire-suspension system. The accuracy of an actuator control of the testing machine is significant for this system. In this paper, we proposed to apply inverse dynamics compensation via ‘simulation of feedback control system’ (IDCS) as an actuator control method for tire-suspension HILS. IDCS is a numerical method to obtain an approximate inverse dynamic via feedback control simulation, using only the forward dynamic model of the system. The performance of IDCS with a multibody model of the hardware part of the HILS system was examined in this paper.

Tracking control of dielectric elastomer actuators for soft robots based on inverse dynamic compensation method

In recent years, the dielectric elastomer actuators (DEAs) have been increasingly used to drive the soft robots. This paper proposes a tracking control method for the DEA based on the inverse dynamic compensation method. Firstly, a dynamical model of the DEA is established to depict its asymmetric hysteresis, rate dependent hysteresis and creep nonlinear behaviors simultaneously. Next, according to the inverse of the dynamical model, an inverse dynamic feedforward compensator (IDFC) is devised to compensate the hysteresis nonlinearity and creep nonlinearity of the DEA. Then, a PI feedback controller is designed to collaborate with the IDFC, which can enhance the robust performance of the whole control system. Finally, the tracking control experiments with different target trajectories are carried out. The root-mean-square errors of all control results are less than 1% and the maximum value of the relative tracking errors is less than 8%, which illustrates that the proposed tracking control method is effective and excellent.

Delayed Teleoperation with Force Feedback of a Humanoid Robot

Teleoperation systems allow the extension of human capabilities to remote-control devices by providing the operator with conditions similar to those at the remote site through a communication channel that sends information from one site to the other. This article aims to present an analysis of the benefits of force feedback applied to the bilateral teleoperation of a humanoid robot with time-varying delay. As a control scheme, we link adaptive inverse dynamics compensation, balance control, and P+d like controllers. Finally, a test is performed where an operator simultaneously handles the locomotion (forward velocity and turn angle) and arm of a simulated 3D humanoid robot to do a pick-and-place task using two master devices with force feedback, where indexes such as time to complete the task, coordination errors, path tracking error, and percentage of successful tests are reported for different time-delays. We conclude with the results achieved.

Inverse dynamics toolpath compensation for CNC machines based on model predictive control

The use of model predictive control (MPC) as a form of inverse dynamics compensation for multi–axis CNC machines, to subdue the inaccuracies incurred by axis inertia and damping, is investigated by both simulation studies and experimental performance analysis using a 3–axis milling machine governed by an open–architecture software controller. The results indicate that MPC is a viable tool for inverse dynamics compensation with a controller sampling frequency f = 1024 Hz running on a 500-MHz processor, with only modest prediction horizons offering excellent performance in terms of feedrate accuracy and contour error suppression. Unlike inverse dynamics schemes based upon linear time–invariant dynamic models, the MPC scheme provides the flexibility to compensate for nonlinear physical effects such as backlash in the machine axes and hard constraints on axis accelerations imposed by motor torque constraint.

A general framework for solving inverse dynamics problems in multi-axis motion control

An inverse dynamics compensation (IDC) scheme for the execution of curvilinear paths by multi-axis motion controllers is proposed. For a path specified by a parametric curve r(ξ), the IDC scheme computes a real-time path correction Δr(ξ) that (theoretically) eliminates path deviations incurred by the inertia and damping of the machine axes. To exploit the linear time-invariant nature of the dynamic equations, the correction term is computed as a function of elapsed time t, and the corresponding curve parameter values ξ are only determined as the final step of the IDC scheme, through a real-time interpolator algorithm. It is shown that, in general, the correction term for P, PI, and PID controllers consists of derivative, natural, and integral terms (the integrand of the latter involving only the path r(ξ), and not its derivatives). The use of lead segments to minimize transient effects associated with the initial conditions is also discussed, and the performance of the method is illustrated by simulation results. The IDC scheme is expressed in terms of a linear differential operator formalism to provide a clear, general, and systematic development, amenable to further adaptations and extensions.

Inverse dynamic compensation via simulation of feedback control system by artificial neural networks for crane system

Inverse dynamic compensation via simulation of feedback control system by artificial neural networks for crane system

Investigation of the milling stability based on modified variable cutting force coefficients

The cutting force signal distortion is caused by the dynamic characteristics of cutting force testing system. In order to handle this issue, we propose two improvements in the traditional inverse filtering technology. Firstly, we use three-spline interpolation method instead of the curve fitting method to fit the frequency response function of the test system which basically improves the accuracy of fitting. Secondly, the low-pass filter is added before the inverse filter to eliminate the influence of the high-frequency noise signal on the cutting force signal. We choose the cavity-free surface of outer covering parts of mold of automobile as research objects. The inverse filter dynamic compensation technology has been used to remove the influence of the dynamic characteristics of the test system and the high-frequency noise on the cutting force signal. The effectiveness of the proposed method is verified by relative milling experiments. Based on the experimentally measured forces after dynamic compensation, the modified cutting force coefficients are obtained using the average milling force method. The variation law of the cutting force coefficients with the axial depth, the radial width, and the feed rate is examined. Based on the modified variable cutting force coefficients, the 3D stability of the ball end milling cutter surface has been obtained using full-discretization approach. Combining the results from the cutting experiment and the nonlinear method, the stability prediction based on the modified variable cutting force coefficient can improve the prediction accuracy. The results provide theoretical support for the optimization of the machining process of the cavity-free surface of outer covering parts of mold of automobile.

Experimental performance analysis of an inverse dynamics CNC compensation scheme for high-speed execution of curved toolpaths

Experimental results from the implementation of an inverse dynamics compensation scheme on a three-axis CNC mill with an open-architecture software controller are presented. The scheme amounts to imposing a continuously variable displacement on the commanded toolpath, which compensates for the physical limitations (inertia and damping) of each machine axis, producing accurate execution of the prescribed toolpath. Numerical values for the dimensionless parameters that characterize the second-order inverse dynamics model are determined by feeding input and output data from machine runs into a system identification software tool. For a basic P-type controller, exact a priori solutions for the modified path geometry are possible, allowing implementation by simple alterations to the real-time interpolator. The experimental results based on a P-type controller indicate that the inverse dynamics scheme is highly effective in suppressing both feed (lag/lead) error and contour error (deviation from the desired path), even at high feedrates along strongly curved toolpaths. The scheme thus provides a practical means of achieving smooth and accurate execution of free-form paths, without appealing to more complicated “active” control strategies.

Inverse dynamics compensation via ‘simulation of feedback control systems'

In many applications within the fields of science, engineering, mathematics, and socio-economics, the ‘inverse problem' (i.e. the problem of determining a system's input from its output) is commonplace. The current paper presents a new concept for solving the inverse problem, which the authors call inverse dynamics compensation via ‘simulation of feedback control systems' (IDCS). IDCS is a numerical method that obtains an approximate inverse dynamic solution via a feedback control simulation, using only the forward dynamic model of the linear or non-linear system. Simulations are ideal environments for feedback control, in the sense that they can be completely noise-free and precisely known, so that the IDCS method can be tuned for the best possible performance. It is seen that IDCS can use the advantages of such ideal control simulation performance in the real world of physical implementations.This paper first introduces the basic idea of IDCS. Then, the effectiveness of the proposed method is demonstrated via three illustrative examples, in which the systems to be controlled have continuous and discontinuous non-linearities. IDCS performance is also investigated via physical experimentation on a non-linear servohydraulic test rig. Finally, extensions of the basic IDCS formulation are introduced which are potentially useful for the solution of additional practical problems.

Testing of dynamically substructured, base‐isolated systems using adaptive control techniques

AbstractExperimental techniques for testing dynamically substructured systems are currently receiving attention in a wide range of structural, aerospace and automotive engineering environments. Dynamic substructuring enables full‐size, critical components to be physically tested within a laboratory (as physical substructures), while the remaining parts are simulated in real‐time (as numerical substructures). High quality control is required to achieve synchronization of variables at the substructuring interfaces and to compensate for additional actuator system(s) dynamics, nonlinearities, uncertainties and time‐varying parameters within the physical substructures. This paper presents the substructuring approach and associated controller designs for performance testing of an aseismic, base‐isolation system, which is comprised of roller‐pendulum isolators and controllable, nonlinear magnetorheological dampers. Roller‐pendulum isolators are typically mounted between the protected structure and its foundation and have a fundamental period of oscillation far‐removed from the predominant periods of any earthquake. Such semi‐active damper systems can ensure safety and performance requirements, whereas the implementation of purely active systems can be problematic in this respect. A linear inverse dynamics compensation and an adaptive controller are tailored for the resulting nonlinear synchronization problem. Implementation results favourably compare the effectiveness of the adaptive substructuring method against a conventional shaking‐table technique. A 1.32% error resulted compared with the shaking‐table response. Ultimately, the accuracy of the substructuring method compared with the response of the shaking‐table is dependent upon the fidelity of the numerical substructure. Copyright © 2009 John Wiley & Sons, Ltd.

A substructure shaking table test for reproduction of earthquake responses of high‐rise buildings

AbstractWhen subjected to long‐period ground motions, high‐rise buildings' upper floors undergo large responses. Furniture and nonstructural components are susceptible to significant damage in such events. This paper proposes a full‐scale substructure shaking table test to reproduce large floor responses of high‐rise buildings. The response at the top floor of a virtual 30‐story building model subjected to a synthesized long‐period ground motion is taken as a target wave for reproduction. Since a shaking table has difficulties in directly reproducing such large responses due to various capacity limitations, a rubber‐and‐mass system is proposed to amplify the table motion. To achieve an accurate reproduction of the floor responses, a control algorithm called the open‐loop inverse dynamics compensation via simulation (IDCS) algorithm is used to generate a special input wave for the shaking table. To implement the IDCS algorithm, the model matching method and the H∞ method are adopted to construct the controller. A numerical example is presented to illustrate the open‐loop IDCS algorithm and compare the performance of different methods of controller design. A series of full‐scale substructure shaking table tests are conducted in E‐Defense to verify the effectiveness of the proposed method and examine the seismic behavior of furniture. The test results demonstrate that the rubber‐and‐mass system is capable of amplifying the table motion by a factor of about 3.5 for the maximum velocity and displacement, and the substructure shaking table test can reproduce the large floor responses for a few minutes. Copyright © 2009 John Wiley & Sons, Ltd.

Non-linear robust control with partial inverse dynamic compensation for a Stewart platform manipulator

This paper presents a non-linear robust control approach for a Stewart platform manipulator with partial inverse dynamic compensation. Firstly, the complete model of the manipulator's dynamics is derived by using a Lagrange method that describes the motion of the upper platform and the six legs. Then, the coupling force caused by the dynamics of the legs is compensated using the Newton–Euler inverse dynamic formula, which makes the compensation algorithm much simpler without computing the complex forward dynamics. A robust tracking control approach is shown to cope with the uncertainties, including the modelling error and the remains of the partial compensation and the disturbances. The controller is designed based on the Lyapunov framework. It is shown that a simple feedback law that achieves the desired tracking performance can be designed by putting the physical property of the compensated system into the Lyapunov function. Finally, to verify the validity of the proposed approach, a simulation result is demonstrated.

Robust Motion Control of Industrial Robot Based on Robot Parameter Identification and Feedforward Control Considering Resonant Frequency

In control application of industrial robot manipulator, a two-inertia resonant system is normally represented as the basic plant model for various control schemes. Various control techniques with partially feedback linearization have been proposed to achieve high performance motion control. The design of such controllers basically relies on system mechanical parameters. The proper parameters of the model cannot be obtained by the parameter identification based on only manipulator force and motion measurements. In this paper, the open-loop resonant frequency characteristic of the flexible joint is employed to identify the proper mechanical parameters of the two-inertia model. The nominal link inertia and spring constant of gear drive can be readily measured by this novel identification method. The identified parameters are used in independent-joint controller design for conventional PD control scheme and robust control scheme to verify the effectiveness of the proposed identification method. Moreover, the accuracy improvement of the proposed robust control scheme based on feedforward inverse dynamic compensation and D-PD position control gives support the validity of the proposed identification method.

Motion Control Strategy for Robot Manipulators in the Neighbourhood of Singularities

This work presents a control strategy applied to robot manipulators operating close to kinematic singularities. Considering the robot to be in contact with the environment, a PD controller is iInplelnented with inverse dynamics compensation to control the robot manipulator. In order to accomlTIodate the forces originated froln the interaction with the environment, the control systelTI includes an impedance loop that modifies the robot's references accordingly. In the vicinity of a singularity, the algorithm generates a fictitious force to which a second impedance function is applied. This causes a small deviation to the original robot trajectory to avoid the singularity region. The algoritlun is based on the minimwn singular value of the Jacobian matrix in order to generate the module and direction of the fictitious force. This strategy is applied to a teleoperation system without time delay

Inverse Dynamics Compensation Method for PWS Mobile Manipulators.

A robot system composed of a robot and a manipulator is called a mobile In this paper a calculation method of inverse dynamics compensation for a power-wheeled-steering(PWS)mobile manipulator is proposed. Newton-Euler method is used for the compensation calculation. A manipulator dirrers from a floor-fixed manipulator in that it moves according to non-holonomic constraints. As the constraints integrate velocity and angular velocity errors of the manipulator on a floor, the errors influence the hand position and orientation of the mounted manipulator. The integrated errors do not disappear even after the dynamical vibration of the manipulator is settled. Therefore, to reduce the integrated errors, the velocity errors of the manipulator should be reduced. We propose a calculation method, and the effects of the method are confirmed by simulation experiments.

非ホロノミック移動マニピュレータの逆動力学補償の効果

非ホロノミック移動マニピュレータの逆動力学補償の効果