Calibration of Closed Loop Controllers for Setting Impedances in Force-Reflecting Systems

A walking assistance apparatus which can promote gait training for motor palsy patients and outdoor walking for the elderly was developed. Our prototype uses a novel spatial parallel link mechanism and restraint free type of equipment. The apparatus supports complete leg alignment, including the soles of the feet from under the soles with flat steps, and assists walking behavior at the ankle, knee, and hip joints simultaneously without the use of Velcro tape. We proposed the control method according to the purpose of the user. For example, to promote gait training, this apparatus can select the impedance control method. User's legs are assisted along the trajectory with the ideal gait as well as walking. To promote outdoor walking for the elderly, this apparatus can select the torque control method. The apparatus calculates the necessary torques of each joint according to the posture and motion of the apparatus and user. In the case of the impedance control method, by adjusting the natural frequency of the ideal dynamic equation for the flat steps under the soles, the user felt it was easier to walk by frequency entrainment. On the other hand, to promote outdoor walking of the user, this apparatus has to be used not only on the flat ground but also on stairs or slopes with freedom behaviors, and it has to make the user feel comfortable. To address this problem, the torque control method proposed to use real-time acceleration data instead of using the template trajectory. By using this method, the subject could walk on the slope and stairs continuously. Finally, %MVC of the user's EMG while walking equipped with this apparatus was measured, and the influence of the difference using between the impedance and torque control method was confirmed by interviewing the subjects. From the result, the impedance control method assisted the motion of kicking the ground, and the torque control method assisted the motion of raising-up the leg. Therefore, the impedance control method is good for gait training, and the torque control method is good for walk promotion.

In this paper, a novel impedance control method is designed for the hydraulic drive unit (HDU) equipped on the hydraulic driven legged robot. First, the position control mathematical model of HDU is built. Next, the HDU performance test platform is introduced and the performance requirements are given. Second, the system load pressure observer is designed and an accurate stiffness control method is proposed by combining the external load force feed forward control with the load force feedback control. Third, the damping control method based on the velocity feedback is designed. Finally, a novel impedance control method is proposed through combining the stiffness control and the damping control. The effects of all techniques listed above have been verified experimentally. Especially, the impedance control effects are verified by comparing the impedance characteristics with the natural characteristics of the second-order mass-spring-damper system. This research indicates that the system characteristics of HDU with the novel impedance control method is well equivalent to that of the second-order mass-spring-damper system, which can solve the stall problem of the robot joint movement process caused by the load force vanish instantaneously and the switch between position control and force control. The above research can provide references for the active compliance control of bionic legged robots.

Control quality of the controller depends on correct tuning of control parameter, and it is directly related to the control effect of whole control system. Aimed at the puzzle that the parameter of controller has been difficult to tune, the paper proposed a sort of optimization model based on immune mechanism for tuning of controller parameters. Firstly it defined the antibody, antigen and affinity of tuning parameter, and secondly explored the process of parameter tuning based on immune mechanism in detail, then explained the tuning method by means of optimizing parameters of PID controller as well as the seven parameters of HSIC controller. Finally it took a high-order process control as the example, and made the simulation to a large time delay process, and to a highly non-minimum phase process as well as HSIC controller. The simulation experiment results demonstrated that it is better in comparison with some other tuning methods for dynamic and steady performance. The research result shows that the proposed method is more effective for controller parameter tuning.

This paper proposes an intelligent massage control system by using multi-fingered robot hand with hybrid impedance control, which is able to create the movement and the force of robot such as the human's massage. Therefore, the various massage points, such as the change of the stiffness of human skin muscle, can be controlled by using impedance control method. The hybrid impedance control is comprised of the two methods of the position-based and the force-based impedance control were applied. The position-based impedance control is used to control the lateral position of massage on the human skin muscle. On the other hand, the force-based impedance control is used to control the force of the vertical direction on human skin muscle. This paper also gives the identification of human skin muscle through robot perception of impedance to decide the parameter of impedance controller. The control strategy using impedance control to implement an adaptive control system is presented, when human condition is changed with soft and hard skin muscle. Effectiveness of massage control system by using multi- fingered robot hand with hybrid impedance control is demonstrator through actual massage experiments of pushing and rubbing motion.

This paper studies the proportional-derivative (PD) control method in the control field, which can be applied in industrial automation, robot control, aerospace, process control, and other fields. This paper discusses the PD control to adjust the motor angle and the fuzzy proportional-integral (PI)-PD control of the brushless direct current (DC) motor. How to apply PD control theory to practice is a part worth exploring. In the traditional control field, proportional-integral-derivative (PID) control parameters cannot adjust the changes of controlled parameters, and the traditional PID control must cooperate with three parameters at the same time to work. Therefore, in this paper, PD control is applied to the adjustment of motor angle, and PI-PD fuzzy control is used to adjust the controller parameters in real time. This method can improve the response speed of the controller, apply the control theory to the actual motor control, and improve the anti-interference ability. This research can improve the application scope of PD control and combine it with a variety of control theories, to achieve a better effect of the control system, optimize the response speed of the motor, and achieve the target speed faster.

This paper proposes a data-driven generalized minimum variance (GMV) regulatory control with constrained controller structure. The proposed approach can obtain control parameters that improve the controller performance based on generalized minimum variance evaluation under the constraint of the FIR (Finite Impulse Response) controller as a linearly parametrized controller. The constrained control structure relaxes the condition that the information of the order of process model is necessary. Whereas, it causes that the resulting control performance severely depends on the initial controller parameters, which is used for the closed-loop system when the initial process input and output data are collected for controller parameter tuning. Thus, the present work updates the controller parameters iteratively by repeating the proposed method. We can expect that the influence of the initial parameters could be reduced by repeating the control parameter update. The theoretical analysis clarifies that repeating the proposed method makes the parameters converge to a certain fixed point under some condition. Finally, a numerical example shows the efficiency of the proposed method.

Autonomy is increasingly demanded by industrial manipulators. Robots have to be capable to regulate their behavior to different operational conditions, without requiring high time/resource-consuming human intervention. Achieving an automated tuning of the control parameters of a manipulator is still a challenging task. This paper addresses the problem of automated tuning of the manipulator controller for trajectory tracking. A Bayesian optimization algorithm is proposed to tune both the low-level controller parameters (i.e., robot dynamics compensation) and the high-level controller parameters (i.e., the joint PID gains). The algorithm adapts the control parameters through a data-driven procedure, optimizing a userdefined trajectory-tracking cost. Safety constraints ensuring, e.g., closed-loop stability and bounds on the maximum joint position errors, are also included. The performance of the proposed approach is demonstrated on a torque-controlled 7degree-of-freedom FRANKA Emika robot manipulator. The 25 robot control parameters (i.e., 4 link-mass parameters and 21 PID gains) are tuned in 125 iterations, and comparable results with respect to the FRANKA Emika embedded position controller are achieved.

A practical way to adjust the input impedance of a rectangular patch antenna is to vary the feed position. The inset-fed patch provides a method of impedance control with a planar feed configuration. The goal of this paper is to further study the inset-fed patch in order to examine the dependence of the input impedance on the inset notch geometry, as well as to realize design tables that show the notch depth to obtain the best input match (minimum |S/sub 11/|) for the inset patch when using a 50 /spl Omega/ feed.

Capacitive impedance control enables a power converter to mimic the voltage-current characteristics of a physical passive capacitor actively; however, existing impedance control methods cannot achieve accurate capacitive control due to parameter errors. This digest proposes a capacitive impedance control method with adaptive parameter capability, which is adaptive to changes in the parameters to maintain the capacitance of the active capacitor to the given reference with high precision. A capacitor bank volume-optimized design procedure of the active capacitor in high-power applications considering reliability design constraints is proposed as well. A 16kVA case study demonstrates the control method and design results.

Multifingered robot hands: Control for grasping and manipulation

This paper mainly studies the modeling, stability analysis and proportional-integral (PI) controller design for a class of discrete-time cascade control systems (CCSs). In the existing CCSs for solving gain of the controller, the controller mostly adopts the proportional (P) controller, but the most commonly used controller in industrial production is PI controller. Based on the actual demand in industry and in order to obtain a better control effect, the design problem of primary and secondary controllers in a class of discrete cascade control is considered, in which the primary controller adopts a PI controller and the secondary controller adopts a P controller. On this basis, the model of cascade control system (CCS) is established. Then, we can create a new Lyapunov functional, the sufficient conditions for the stability of the system is given. Then, the collaborative design method of primary PI controller and secondary P controller is given by using linear matrix inequality (LMI) technique. Finally, a simulation example of a main steam temperature with CCS structure is given to demonstrate the effectiveness of the method. The PI controller is better than the existing P controller, this method has not only the rapidity of P control, but also the ability of integral control to eliminate steady-state errors. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Note to Practitioners</i> — The inspiration of this paper comes from the adjustment of plant controller parameters. The PI controller is the most widely used controller in the existing industrial production, but the adjustment of proportional and integral parameters of the controller is a very troublesome thing. In order to obtain a better controller parameters, a professional engineer may spend a whole day to adjust the parameters. This paper can design the solution of the primary and secondary controller parameters to stabilize the CCS at the same time by LMI technique, which can greatly reduce the work of adjusting the controller parameters. Through simulation, we can know that this method can make the system stable, which shows this method is feasible.

This paper proposes an intelligent massage control system by using multi-fingered robot hand with hybrid impedance and force control, which is able to create the movement and force of robot to behave as similar as the human’s massage. Therefore, the various massage points, such as the changing of hardness and softness of human skin muscle condition, can be appropriately controlled by using hybrid impedance and force control method. The impedance control is used to control the lateral position of massage on the human skin muscle. The perpendicular direction one, while force control is carried out for the vertical direction on human skin muscle. This paper also gives a modeling of human skin muscle through robot perception of impedance to decide the parameter of impedance controller. The control strategy using a hybrid impedance and force control to implement an adaptive control system is presented, when human condition is changed with soft and hard skin muscle. For the robot fingertip force, PI servo compensation is used together with impedance control. Based on using both impedance and PI servo compensation, the effectiveness of the massage position and force control is shown through actual massage motion experiments.

Frequency damping control is a crucial aspect of islanded microgrids utilizing multiple virtual synchronous generators (VSGs). This paper studies the effects of line impedance mismatches and transient frequency out-of-sync leading to frequency interactive oscillation in VSGs. To address this issue, we propose a distributed interactive damping and zero-error control method that utilizes sparse communications. The objective of this method is to effectively suppress frequency oscillation by minimizing the differences in frequency dynamics among all VSGs. By implementing this approach, a low rate of change of frequency (RoCoF), accurate active power sharing, and zero frequency deviation are ensured. Through dynamic performance analysis, frequency characteristic analysis, and stability analysis based on LaSalle’s invariance principle, we demonstrate significant improvements in system stability, as well as dynamic and steady state performances. Finally, simulation and experimental results obtained under load changes, short-circuits, and communication faults validate the effectiveness of the proposed control method.

In this paper, a new control scheme, the artificial neuro fuzzy inference system (ANFIS) gain scheduled genetic algorithm (GA) based PID is proposed for continuous stirred tank reactor (CSTR). CSTR is a highly nonlinear process that exhibits stability in certain region and instability in some regions. The proposed control scheme implements the characteristics of the genetic algorithm&apos;s (GA) global optimization to optimize the PID&apos;s three control parameters: kp, ki, kd, to obtain the best control effect by minimizing integral square error online. The GA tuned PID controller parameters are gain scheduled using ANFIS. ANFIS gain- scheduling is a special form of neuro-fuzzy control that uses linguistic rules and fuzzy reasoning to determine the controller parameter transition policy for the dynamic plant subject to large changes in its operating state. Simulation result shows the feasibility of using the proposed controller for the control of the dynamical nonlinear CSTR.

A unicycle model of control a mobile robot is a simplified modeling approach modified from the differential drive mobile robots. Instead of controlling the right speed, and the left speed, of the drive systems, the unicycle model is using and as the controller parameters. Tracking is much easier in this model. In this paper, the dynamic of the robot parameter is controlled using two blocks of Proportional-Integral-Derivative (PID) controllers. The gains of the PID are firstly determined using particle swarm optimization (PSO) in offline mode. After the optimal gain is determined, the tracking of the robot’s trajectory is performed online with optimal PID controller. The achieved results of the proposed scheme are compared with those of dynamic model optimized with genetic algorithm (GA) and manually tuned PID controller gains. In the algorithm, the control parameters are computed by minimizing the fitness function defined by using the integral absolute error (IAE) performance index. The simulation results obtained reveal advantages of the proposed PSO-PID dynamic controller for trajectory tracking of a unicycle type of mobile robot. A MATLAB-Simulink program is used to simulate the designed system and the results are graphically plotted. In addition, numerical simulations using 8-shape as a reference trajectory with several numbers of iterations are reported to show the validity of the proposed scheme.