Controller Design and Experimental analyses of Two-Robot Coordination System

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.

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.

In the present paper, the objective of hybrid impedance control is specified and a robust hybrid impedance control approach is proposed. Based on the concept of hybrid control, the task space is decomposed into position and force controlled subspaces. Impedance control is used in the position controlled subspace. Desired inertia and damping are applied in the force controlled subspace to meliorate the dynamic behavior of robot manipulator. Robust controller using the variable structure model reaching control (VSMRC) is introduced that can realize the objective impedance in the sliding mode in finite time. In order to overcome the chattering effect due to sliding mode approach, fuzzy logic methodology is employed in the control system. In addition, the reaching transient response is undertaken with prescribed quality. Simulating the control system for a 6DOF PUMA560 robot confirms the validity and effectiveness of the proposed control system.

This article presents a comparative study between the hybrid impedance control approach and the impedance force control approach with neural networks compensation of manipulator modeling errors. The proposed algorithm consists of an outer hybrid impedance control loop that generates the reference (target) acceleration to an inner inverse dynamics control loop. In order to improve the controller robustness, a compensation action of the manipulator modeling errors is introduced, acting on the target acceleration. This compensation action is based on a neural network model achieved by minimizing the modeling errors along the manipulator trajectory. The neural network algorithm uses an error training signal to model errors, that is minimized along the trajectory. The performance of the hybrid impedance control system with neural network compensation, is compared with the impedance force controller with neural network compensation, and is illustrated by computer simulations with a two degree-of-freedom PUMA 560 robot, whose end-effector is forced to move along a frictionless surface located perpendicular to the horizontal plane. The results obtained reveal even better performance when the desired force profile is not constant along the trajectory. This situation is very important in fine motion tasks where the desired force must have a varying profile along the trajectory, namely at the beginning and the end of the task. The results have also shown accurate force tracking and position control, even when significant uncertainties in the robot dynamic model are assumed.

Chapter Twelve - Impedance control applications in therapeutic exercise robots

According to the all-pervading theory, the best strategy for multiaxis compliant control system is the famous hybrid movement/force control. Until now, the typical way to get it inclines to integrate force control with movement control into one numerical control (NC) interpolator. The more axes being taken for the interpolator, the lower calculating and computerizing speed and the greater errors are. Furthermore, the errors of movement control, including the position errors and pose errors, would inevitably disturb the processing of force control for their coupling relationship. In this paper, the orthogonal movement/force servo strategy is brought forward based on the orthogonality relation of force control and movement control. Combining with the processing of aspheric surfaces polishing, the paper develops a new three-axis computer numerical control (CNC) compliant polishing method and system by the hybrid orthogonal movement/force servomechanism, in which the force controlling and movement controlling are taken in its orthogonal complement space, respectively. Experiments show that this new polishing system is of great robustness for the change of slope and curvature of the aspheric surfaces and it can polish aspheric surfaces to get ultrasmooth surfaces at nanoscale.

This paper considers a power assist system of elbow as an example of human-assist system and describes impedance control of it. The assist system is required not only to assist the movement of elbow but also to be strictly stable. Impedance control based on position control is often used for the assist devices because the control system is simpler than that of the devices based on force control. But if the impedance parameters are made to be small in order to get good maneuverability, the system becomes unstable because of the delay of the position control system especially when the assisted tool touches high stiffness environment such as a wall. So, an impedance control method based on position control with passive elements is proposed. As a result, the stability and the effects on time delay of the proposed system showed good performance.

Human assist devices are expected to be developed in the field of welfare, home, factory and so on. The devices are required to not only to assist the human but also to be strictly stable. Impedance control based on position control is often used for the human assist devices because the control system is simpler than that of the devices based on force control. But if the impedance parameters are made to be smaller in order to get good maneuverability, the system becomes unstable because of the delay of the position control system especially when the assisted tools touch high stiffness environment such as a wall. In this paper, we propose an impedance control method based on position control by employing passive elements such as a mass, a spring and a damper. Then we show in a simulation that the system controlled by the proposed method with very low impedance parameters is stable even if the system touches a high stiffness environment.

This paper proposes a method to design a force controller based on frequency characteristics. Generally, force control algorithms are classified into two types, the explicit force control algorithms such as hybrid position/force control and the implicit force control algorithms such as impedance control. The explicit force control algorithms control the contact force directly, while the implicit force control algorithms control the manipulator motion-force relation. Recently, Goldenberg (1992) and others have shown the equivalence of these two types of algorithms. In this paper, we propose a method to design an explicit force controller based on its equivalence to the impedance controller so that the resultant control system has desired frequency characteristics. The method is applied to a manipulator with one-degree-of-freedom and experimental results illustrate the effectiveness of the proposed method. >

The best exoskeleton control strategy depends on the task, motivating the development and analysis of an exoskeleton capable of position, force, and impedance control. In this paper, we implement and compare the three controller types via sliding mode control on a custom-built pneumatic cylinder ankle exoskeleton. To evaluate each controller's performance, the exoskeleton was tested on the benchtop and with human subject experiments. With the position controller, the exoskeleton achieved an root-mean-square error (RMSE) of under 5 deg for both the benchtop and human tests. It had a bandwidth of approximately 12 rad/s. The force controller tracked sinusoidal trajectories acceptably well at low frequencies (15% of force range at 6 rad/s), with a bandwidth of approximately 24 rad/s. The error was significantly higher (RMSE of 24% of force range) for the more biologically relevant trajectory. The impedance controller demonstrated the desired spring-like behavior, with position RMSE generally under 5 deg compared to expected position. All three controllers worked equally well for benchtop and human tests. Thus, a pneumatically powered ankle exoskeleton with sliding mode control is capable of accurate position and impedance control and is capable of marginally acceptable force control.

In this paper, the problem of position and force control of a robotic manipulator in contact with the environment is considered. The Hybrid Impedance Control (HIC) methodology is employed to control the position of the end-effector in such a way that the robot exhibits a desired dynamic property and hence desired Impedance which in turn results in tracking the interaction force. It is assumed that the robot has unknown dynamics, hence an adaptive HIC is used to control the robot manipulator. The environment is modeled as a spring to be used in the force control directions. The Lyapunov's theorem is used to show the stability of the closed-loop system obtained by the proposed adaptive law. The effectiveness of the proposed approach is demonstrated via simulations performed on a three-link articulated manipulator.

Robotic force control is a core research direction in robotics technology. For tasks such as polishing and assembly, it requires not only precise motion control but also compliant force control by adjusting output force and torque. Traditional impedance control can ensure accuracy in a single environment, but it is limited by the difficulty in accurately acquiring parameters in complex environments; although variable impedance control can adapt to the environment, it faces challenges in control law design. This paper integrates the extended Twin Delayed Deep Deterministic Policy Gradient (ex-TD3) algorithm with impedance control, proposing an ex-TD3-based intelligent impedance control optimization algorithm. A Python-MATLAB/SimMechanics co-simulation platform is established to verify its effectiveness. The experiment adopts a scenario where the robot moves linearly along the z-axis, with fixed environmental stiffness and the desired tracking force changing in stages over time. The model training is iterated for 300 episodes, after which the reward tends to stabilize and the control strategy converges. Experimental results show that, compared with the traditional adaptive impedance control algorithm, the proposed algorithm in this paper exhibits faster force response, smaller force fluctuations during force step changes, smoother force output throughout the process: the maximum overshoot of force control decreases from 6.21N to 1.33N (a reduction rate of 77.63%), and the maximum position tracking error is reduced by 69.5%. With the above optimized design, this study significantly improves the energy efficiency and long-term operational sustainability of mechatronic systems; its precise control of force overshoot and position tracking error effectively reduces mechanical losses and unnecessary energy consumption during the system’s dynamic interaction with the environment.

PurposeThis paper aims to present a smooth transition adaptive hybrid impedance control for compliant connector assembly.Design/methodology/approachThe dynamics of the manipulator is firstly presented with linear property. The controller used in connector assembly is inspired by human operation habits in similar tasks. The hybrid impedance control is adopted to apply force in the assembly direction and provide compliance in rest directions. The reference trajectory is implemented with an adaptive controller. Event-based switching strategy is conducted for a smooth transition from unconstrained to constrained space.FindingsThe method can ensure both ideal compliance behaviour with dynamic uncertainty and a smooth transition from unconstrained to constrained space. Also, the method can ensure compliant connector assembly with a good tolerance to the target estimation error.Practical implicationsThe method can be applied in the connector assembly by “pushing” operation. The controller devotes efforts on force tracking and smooth transition, having potential applications in contact tasks in delicate environment.Originality/valueAs far as the authors know, the paper is original in providing a uniform controller for improving force and position control performance in both unconstrained and constrained space with dynamic uncertainty. The proposed controller can ensure a smooth transition by only adjusting parameters.

Sum-of-squares-based robust H∞ controller design for discrete-time polynomial fuzzy systems

Robotic systems have significantly transformed the landscape of minimally invasive surgery, offering enhanced precision, reduced recovery times, and improved patient outcomes. These systems have evolved from simple mechanical tools to sophisticated platforms integrating advanced control algorithms and real-time feedback mechanisms. This paper provides a comprehensive overview of the role of robotic systems in minimally invasive surgery, exploring the various benefits, inherent risks, and the challenges associated with their adoption and development. We examine the technical aspects of robotic control systems, such as kinematics, force control, and haptic feedback, which enable greater surgical accuracy. Despite these advantages, challenges such as system complexity, high costs, and ethical concerns remain significant barriers to widespread adoption. The future of robotic surgery lies in overcoming these obstacles, with advancements in system miniaturization and further refinement of control systems poised to enhance the efficacy and accessibility of robotic platforms. This paper explores the role of robotic systems in minimally invasive surgery, focusing on three key areas: bronchoscopy and ureteroscopy. By reviewing the benefits, risks, case studies, and future directions of these technologies, the paper seeks to provide an in-depth understanding of how robotic systems are shaping the future of surgery. Key words: Robotic Surgery, Minimally Invasive Surgery, Robotic Control Systems, Surgical Precision, PID Control, Kinematics, Inverse Kinematics, Forward Kinematics, Dynamic Control, Force Control, Impedance Control, Surgical Robotics, Haptic Feedback, Robotic Arm, Robotic Surgery Benefits, Robotic Surgery Risks, Robot-Assisted Surgery, Surgeon Console, Real-Time Feedback, Surgical Training, Robotic System Development, System Testing, Clinical Trials, Surgical Robot Performance, Robotics in Urology, Telepresence Surgery, Robotic Surgery Cost, Robotic Surgery Future Directions.