Realization of precise force control using both 2‐DOF control and learning control

Collagen is a major structural protein in the human body.It not only provides connective tissues such as ligaments and tendons with toughness and strength but it also constitutes the biomechanical scaffold for cell attachment in the extracellular matrix. Collagen molecules aggregate to form collagen fibrils. Tensile tests on individual collagen fibrils reveal a strongly non-linear stress-response to deformation with the tensile modulus reaching the gigapascal range. But not only that, collagen fibrils have been found to be viscoelastic which means collagen fibrils have both elastic and viscous characteristics. However, direct measurement of viscoelastic material properties in tension is only possible with force-controlled tensile tests, which can not be conducted with state-of-the-art methods. In this paper, we report the first force-controlled tensile tests of individual collagen fibrils. To account for the non-linear material characteristics, high responsiveness in the force control and robustness about a property change of the collagen fibril are needed. Therefore, a two-degrees-of-freedom (2-DOF) controller is applied for force control with high responsiveness. The 2-DOF controller is composed of feedforward (FF) and feedback (FB) controllers. In addition, a modeling error compensation is implemented for robustness. The modeling error is calculated from the difference between the actual force response measured by the sensor and the ideal force response calculated from the plant model. The validity of the proposed control method is confirmed from simulation and experimental results.

This paper presents analysis, design and simulation of one degree-of-freedom (1DOF) and two degrees-of-freedom (2DOF) controllers for the indirect field orientation control (1FOC) of induction machine drive system. To achieve zero steady state error, minimum overshoot and minimum settling time, (good dynamic response for disturbance rejection and set point tracking), 1DOF and 2DOF controllers are designed and analyzed. The design of these controllers is developed based on the transfer function of the induction machine in the synchronous reference frame at field orientation control (FOC). The 1DOF controller is an integral plus proportional (IP) configuration while the 2DOF controller consists of proportional plus integral (PI) type in the feedback loop and lead/lag compensator in the feedforward loop. To verify the design of controllers and system performance, the drive system is simulated using SIMULINK for MATLAB. The desired current and speed tracking control performances of the drive can be preserved under wide operating range and good load regulating performance can also be obtained. The dynamic performance of the drive system for different operating conditions is studied with application of IP and 2DOF controllers. Taking into consideration the parameter variations of the induction machine, the dynamic performance have been studied under load changes and set-point variations. The simulation results are provided to demonstrate the effectiveness of the proposed controllers.

This paper focuses on the two degree-of-freedom (2DOF) control design problem for high-speed and precision tracking system. The requirements for tracking resolution, bandwidth are transformed to the H ∞ norm minimizing problem of tracking error. A 2DOF control design approach based on an improved H ∞ linear matrix inequalities (LMI) representation is proposed. The design approach offers a new LMI to obtain the feedforward controller and feedback controller in 2DOF control scheme. The results of simulation experiment demonstrates the proposed approach could obtain a better tracking performance compared with conventional H ∞ 2DOF design based on bounded real lemma.

Background: The conventional method using one-degree-of-freedom (1DOF) controller for Permanent Magnet Synchronous Motor (PMSM) servo system has the trade-off problem between the dynamic performance and the robustness. Methods: In this paper, by using H∞ control theory, a novel robust two-degree-of-freedom (2DOF) controller has been proposed to improve the position control performance of PMSM servo system. Using robust control theory and 2DOF control theory, a H∞ robust position controller has been designed and discussed in detail. Results: The trade-off problem between the dynamic performance and robustness which exists in one-degree-of-freedom (1DOF) control can be dealt with by the application of 2DOF control theory. Then, through H∞ control theory, the design of robust position controller can be translated to H∞ robust standard design problem. Moreover, the control system with robust controller has been proved to be stable. Conclusion: Further simulation results demonstrate that compared with the conventional PID control, the designed control system has better robustness and attenuation to the disturbance of load impact.

This study presents a novel adaptive robust control scheme to achieve a fast and accurate tracking performance in direct-drive (DD) systems under parameter and load uncertainties. The control combines an outer loop based on H∞ model matching (MM) in a two-degree-of-freedom (2-DOF) control structure, with an adaptive cancellation loop to increase torque ripple suppression further for improved tracking performance. A modified H∞ MM 2-DOF approach is taken by designing both the feedback loop and reference controller to achieve an improved tracking performance in the sense of H∞ MM criterion with integral action, while the robustness of the system is naturally satisfied by the 2-DOF control structure. Experimental results taken on a permanent magnet synchronous motor (PMSM) driven direct-drive system demonstrate a good tracking performance under a variety of reference trajectories. The results also demonstrate the robustness of the method against payload uncertainties and torque pulsations, except for the cogging torque components around the corner frequency. To improve attenuation of cogging torque terms further, the H∞ based outer loop is combined with an adaptive cancellation scheme derived based on the Lyapunov criteria. The developed adaptive robust control scheme demonstrates an improved robustness and tracking performance over a large frequency range.

To improve H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> tracking control performance of continuous linear time-invariant (LTI) systems with uncertainty, a mixed H2/H∞ robust inversion based 2DOF control approach is proposed in this paper. In the proposed control approach, an optimal inversion-based feedforward controller is designed to minimize the weighted H2 norm of tracking error in the presence of worst system uncertainty. A robust feedback controller is designed to minimize the weighted H2 norm of tracking error and satisfy requirement of H∞ performance of entire control system. The simulation experiment results demonstrate that the proposed approach not only renders the requirement of H∞ performance satisfied, but also has better H2 tracking performance compared with the traditional inversion-based 2DOF control and H∞ mixed sensitivity feedback control approaches.

This paper presents the position tracking performance of an electro-hydraulic hydraulic actuator (EHA) system by using a discrete sliding mode control (DSMC). A point-to-point trajectory is used in the experimental works to evaluate the performance of the DSMC which is design in two-degree-of-freedom (2-DOF) control structure. The design consists of DSMC and a feed forward controller. The control law is derived from the reaching law concept and its parameters are determined methodically based on the identified model. Experimental results reveal that the DMSC with 2-DOF control structure is highly robust and capable to deal with the uncertainties and disturbances occur during the position tracking control for different point of trajectories. It is also shows that the proposed controller can achieve better tracking performance as compared to conventional LQR and PID controller.

This paper describes sound transmission reduction control through thin plate by using piezoelectric ceramic sensors and actuators, both of which are bonded on both surfaces of the plate. 2-DOF control system is introduced to reject the effect of bending vibration of the periodic component and continuously distributed component over the broad frequency range. The adaptive feedforward control is realized by using FIR filters and LMS system identification algorithm. The filtered epsilon with delay system is applied to cope with the non-minimum phase of the identified feedforward control systems. The internal model control is introduced to the feedback control system, which are constructed basically with the direct velocity feedback (DVFB) system. The internal model control was efficient to suppress the howling instability to occur frequently in case of high feedback gain. The substantial reduction of the sound radiation from the plate in the control experiment proves the effectiveness of the 2 DOF control system.

This paper presents a design method for discrete-time parallel with continuous-time design for the two degree of freedom (2DOF) control system using PID (Proportional-Integral-Derivative)×(n-2) stage PD as a cascade controller for a class of nth order plant. Both, transient and steady state response specifications are suddenly met when the forward controller is employed. The root loci of this method are shown that the closed loop system is robustly stable with excellence.

Hardware-in-the-Loop tests have become a key factor in decreasing development time of various drive systems. In this context, high performance test beds, where feedback control plays a major role, are necessary to meet the demanding requirements such as real driving emissions in the automotive industry. Particularly for combustion engine test beds, periodic combustion strokes cause large oscillations in different measurement signals on engine test beds, which causes severe problems since conventional controllers try to compensate for these periodic disturbances. The control settings are a trade-off between fast reference tracking and undesirably strong disturbance rejection, which may compromise test results. An ordinary two-degree-of-freedom (2-DOF) control with flatness-based feedforward control produces relief in separating reference and disturbance behavior but cannot handle input constraints. Thus, a model predictive feedforward controller (MPFFC) in combination with the 2-DOF strategy is introduced for high-dynamic speed control in this contribution. The MPFFC generates optimal input and output trajectories, which respect constraints of the system. Fast reference tracking is achieved without the risk of falsification by high feedback. Comparisons between the proposed method, a simple feedback and a standard 2-DOF controller with a conventional flatness-based feedforward control are performed on a state-of-the-art 4-cylinder engine test bed. The experiments constitute a rare implementation of a MPFFC on a real system and demonstrate its capabilities of separating reference and disturbance response as well as taking advantage of certain situations to even further improve reference tracking speed.

This paper addresses the problem of design of a two degree of freedom (2-DOF) PID controller for time delay systems. The proposed approach is to design 2-DOF PID controller using a novel method which combines model order reduction, approximate model matching (AMM) concepts as well as optimisation techniques. The conventional PID controllers are usually in 1-DOF structure. The problem of finding the parameters of the 2-DOF PID controller is formulated as that of obtaining the solution of a set of non-homogeneous linear equations. The proposed method not only ensures the stability of the closed loop system with a 2-DOF PID controller but also satisfies the required performance criteria. The developed method does not pose any restriction either on the order of the model or on the structure/order of the controller transfer function. Moreover, this method is computationally simple and easy to implement. Simulation results demonstrate the effectiveness of the proposed method.

This paper proposes a nature inspired, meta-heuristic optimization technique to tune a proportional-integral-derivative (PID) controller for a robotic arm exoskeleton RAX-1. The RAX-1 is a two-degrees-of-freedom (2-DOFs) upper limb rehabilitation robotic system comprising two joints to facilitate shoulder joint movements. The conventional tuning of PID controllers using Ziegler-Nichols produces large overshoots which is not desirable for rehabilitation applications. To address this issue, nature inspired algorithms have recently been proposed to improve the performance of PID controllers. In this study, a 2-DOF PID control system is optimized offline using particle swarm optimization (PSO) and artificial bee colony (ABC). To validate the effectiveness of the proposed ABC-PID method, several simulations were carried out comparing the ABC-PID controller with the PSO-PID and a classical PID controller tuned using the Zeigler-Nichols method. Various investigations, such as determining system performance with respect to maximum overshoot, rise and settling time and using maximum sensitivity function under disturbance, were carried out. The results of the investigations show that the ABC-PID is more robust and outperforms other tuning techniques, and demonstrate the effective response of the proposed technique for a robotic manipulator. Furthermore, the ABC-PID controller is implemented on the hardware setup of RAX-1 and the response during exercise showed minute overshoot with lower rise and settling times compared to PSO and Zeigler-Nichols-based controllers.

This paper is concerned with Iterative Feedback Tuning (IFT) for Two-degree-of- freedom (2-DOF) system. The IFT is a data-driven method for tuning controller parameters, which uses the closed-loop system input-output data directly, and without establishing a mathematical model for the controlled system. The design of control system is a multi-objective problem, so a 2-DOF control system naturally has advantages over a one-degree-of- freedom (1-DOF) control system. When tuning 2-DOF system controllers, two-step method is firstly concerned. While in this paper, the application of IFT method in a 2-DOF control system is studied, which can make controllers’ parameters tuned at the same time, and the IFT method is more accurate and efficient in tracking performance and robustness. The feasibility and effectiveness of the method are verified by numerical simulation and comparison.

This paper presents an evolutional compensator design for motion control systems using genetic algorithms (GAs). The control system is composed of a robust two-degrees-of-freedom (2DOF) compensator based on the coprime factorization description. A feedback compensator in the 2DOF control system is theoretically designed under the /spl mu/-Synthesis framework to ensure the robust stability because the real plant mechanism includes structured uncertainties, e.g., the frequency perturbations of vibration modes. On the other hand, a feedforward compensator is optimized by GA paying attention to the robust servo characteristics against the mechanical parameter variations, where the structuring and parameterization of the compensator can be autonomously achieved to satisfy the desired servo characteristic with the resonant vibration suppression performance. The effectiveness of the proposed controller design has been verified by experiments using a prototype.

A two-axis, recuperated cycle micro-gas turbine (MGT) system for biomass gas is developed. The rated specifications of the MGT are as follows, pressure ratio of 2.7, turbine inlet temperature of 1120K, and output power of 5kW. The system consists of three components: the MGT power-generating system, control system and mock biomass gas supply system. The original two-stage combustor and H infinity system controller used in this system are discriminative. Since the gaseous fuel converted from biomass has a low heat quantity, the combustor is designed to achieve both high combustion efficiency and low NOx emission for lower calorific fuel. In the combustor, a stable tubular flame combustion of city gas in the first stage supplies burned gas, which has enthalpy and activated radicals, to the second stage and enables stable ignition and combustion of biomass gas and air premixture. In addition, because the gas composition of biomass gas is also affected by the sources, the gasification method, and the gasifying condition, the system controller is required to absorb fuel fluctuation while meeting the demanded output. Hence, the H infinity algorithm is employed as a system controller because of its robustness against disturbances from the unpredictable fuel component fluctuation. Using this MGT system, an operation test was carried out with mock biomass gases. The rotational speed of the power turbine could be kept almost constant with both mock fermentation gas and pyrolysis gas as the second-stage fuel, and NOx emission was 50ppm when load was increased to a rated power of 5kW. When the second-stage fuel composition changed from 100% methane to 50% methane and 50% CO2 at a certain speed, the power turbine speed could also be kept constant. The H infinity controller is compared with the 2-DOF PID controller for secondary fuel concerning the response to varying load. The former shows slightly better performance than the 2-DOF PID controller.