Chapter Twelve - Impedance control applications in therapeutic exercise robots

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.

Aerial manipulation of objects has a number of advantages as it is not limited by the morphology of the terrain. One of the main problems of the aerial payload process is the lack of real‐time prediction of the interaction between the gripper of the aerial robot and the payload. This paper introduces a digital twin (DT) approach based on impedance control of the aerial payload transmission process. The impedance control technique is implemented to develop the target impedance based on emerging the mass of the payload and the model of the gripper fingers. Tracking the position of the interactional point between the fingers of gripper and payload, inside the impedance control, is achieved using model predictive control (MPD) approach. The developed on‐board DT offered a model where interaction with the unknown payload and aerial robot dynamics is informed. Beside this, the results showed the ability of the introduced DT to foretell the conditions of the forces acting on the payload which helped to predict the situation of aerial manipulation process. Additionally, the results showed that the DT model could detect real‐time errors in the physical asset.

Physiotherapy is the treatment to recover a patient’s mobility and limb function after an injury, illness, or disability. Rehabilitation robots can be used to replace human physiotherapists. To ensure safety during robot physical therapy, the patient’s limb needs to be controlled to track a desired joint trajectory, and the torque due to interaction force/torque needs to be measured and regulated. Therefore, hybrid impedance and admittance with position control (HIPC) is required to track the trajectory and simultaneously regulate the contact torque. The literature describes two structures of HIPC: (1) a switched framework between admittance and impedance control operating in parallel (HIPCSW); and (2) a series connection between admittance and impedance control without switching. In this study, a hybrid adaptive impedance and position-based admittance control (HAIPC) in series is developed, which consists of a proportional derivative-based admittance position controller with gravitational torque compensation and an adaptive impedance controller. An extended state observer is used to estimate the interaction joint torque due to human stiff contact with the exoskeleton without the use of force/torque sensor, which is then used in the adaptive algorithm to update the stiffness and damping gains of the adaptive impedance controller. Simulation results obtained using MATLAB show that the proposed HAIPC significantly reduces the mean absolute values of the actuation torques (control inputs) required for the shoulder and elbow joints in comparison with HIPC and HIPCSW.

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.

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.

The interaction force control problem for the object manipulated by the dual-arm manipulator with the unknown environment is addressed in this paper. An adaptive dual-loop impedance control scheme is designed to meet the three control targets, including the trajectory tracking control of the object, the internal force control of the object with the two arms, and the interaction force control of the object with the unknown environment. Firstly, an adaptive variable impedance control method is proposed in the outer loop to copy with the unknown stiffness and position of the environment. Secondly, an impedance control scheme based on the internal force is designed in the inner loop to plan the internal force and the modified position supplied with the outer-loop control. Thirdly, to realize the reference trajectory supplied with the inner-loop control, the virtual decomposition control (VDC) method is incorporated, which is a recursive adaptive control progress, so that the unknown dynamics of the manipulators is acceptable and the computation complexity is also very low to satisfy the real-time control requirement. The stability verifications of the inner-loop impedance control and the VDC method are given based on the Lyapunov method, and the stability analysis of the outer-loop impedance control is obtained using the Routh criterion. Finally, a plane dual-arm robotic manipulator with three degrees of freedom is used to verify the effectiveness of the proposed control scheme.

Introduction With the increasing requirements for performance and safety of lower limb exoskeleton rehabilitation robots, researchers are exploring various active compliance control strategies to improve the compliance of control and enhance safety and effectiveness of rehabilitation training. The focus of this paper is to evaluate existing active compliance control strategies applied to lower limb exoskeleton rehabilitation robots, highlighting their principles, key technologies, and performance. Areas covered Literature searches were conducted in PubMed and Web of Science from 2000 to 2025, starting with the broad keyword ‘active compliance control strategy’ and narrowing down to specific aspects such as ‘impedance control’. Sixty-nine articles were reviewed, and eight active compliance control strategies were divided into three categories according to their core principles: impedance control (n = 18), force, and position hybrid control (n = 27) and machine learning-based hybrid control (n = 24). Their applications in five types of lower limb exoskeleton rehabilitation robots are outlined. Expert opinion Active compliance control strategies for lower limb exoskeleton rehabilitation robots are necessary for safe human-robot interaction and assist-as-needed implementation. This paper envisions the concept of an active compliance controller that covers the entire rehabilitation cycle, ensuring that the robot is continuously aligned with the patient’s rehabilitation needs.

Advancements in robotic systems hold significant promise for enhancing spinal interventions. Despite this potential, the integration of robotic platforms in spine surgeries remains limited to only a few procedures. This paper presents a variable impedance control scheme within a shared-control framework to enhance haptic feedback during spinal surgeries. The system allows surgeons to guide the robot while dynamically adjusting stiffness based on contact forces and human intent, using electromyography signals. This adaptive control offers real-time guidance during interactions with different materials, serving as a safety measure to safeguard delicate structures encountered during surgical maneuvers. The system comprises a 7-DoF robotic manipulator with a 6-axis force/torque sensor and an 8-channel EMG sensor. Technical validation and a user study assessed performance compared to constant parameter (CIC) and linear variable (LVIC) impedance control methods. Results showed reduced contact force ( vs CIC's and LVIC's ) and in-contact displacement ( vs CIC's and LVIC's ), when interacting with delicate materials, minimizing the risk to critical anatomical structures. Additionally, a user survey confirmed that the proposed system improved haptic perception and control while preventing undesired movements during interactions with various tissues and structures.

Rehabilitation robots play an important role in the rehabilitation field, and effective human-robot interaction contributes to promoting the development of the rehabilitation robots. Though many studies about the human-robot interaction have been carried out, there are still several limitations in the flexibility and stability of the control system. Therefore, we proposed an advanced adaptive control method for lower limb rehabilitation robot. The method was devised with a dual closed loop control strategy based on the surface electromyography (sEMG) and plantar pressure to improve the robustness of the adaptive control for the rehabilitation robots. First, in the outer loop control, an advanced variable impedance controller based on the sEMG and plantar pressure was designed to correct robot's reference trajectory. Then, in the inner loop control, a sliding mode iterative learning controller (SMILC) based on the variable boundary saturation function was designed to achieve the tracking of the reference trajectory. The experiment results showed that, in the designed dual closed loop control strategy, a variable impedance controller can effectively reduce trajectory tracking errors and adaptively modify the reference trajectory synchronizing with the motion intention of patients; the designed sliding mode iterative learning controller can effectively reduce chattering in sliding mode control and excellently achieve the tracking of rehabilitation robot's reference trajectory. This study can improve the performance of the human-robot interaction of the rehabilitation robot system, and expand the application to the rehabilitation field.

Актуальність. За останні десятиліття військові конфлікти породили збільшення кількості військових з ампутаціями, що підкреслює важливість використання робототехніки в їхній фізичній реабілітації для покращення якості життя та соціальної інтеграції. Використання робототехніки у фізичній реабілітації військових з ампутаціями має велике значення у зв’язку зі зростанням кількості військових, які отримали ампутації внаслідок конфліктів та бойових дій. Ця тема актуальна, оскільки вона спрямована на поліпшення якості життя та повернення до нормального фізичного функціонування військовослужбовців, які отримали такі важкі травми. Мета роботи полягає в дослідженні ефективності та переваг використання робототехніки в процесі фізичної реабілітації військових з ампутаціями, зокрема в оцінці впливу таких технологій на покращення мобільності, якості життя та соціальної адаптації пацієнтів. Матеріали та методи. Здійснювався систематичний пошук наукових джерел, які містять аналіз і синтез теоретичних підходів до використання робототехніки у фізичній реабілітації військових з ампутаціями. Для цього були використані різноманітні наукові джерела, що дозволило узагальнити та оцінити сучасні методи та підходи у цій галузі, спрямовані на поліпшення якості реабілітації та соціальної адаптації військових з ампутаціями. Результати дослідження. Стаття присвячена дослідженню використання робототехніки у фізичній реабілітації військових з ампутаціями. Зокрема, розглянуто актуальність цієї теми у зв’язку зі зростанням кількості військовослужбовців, які стають жертвами ампутацій унаслідок збройних конфліктів та бойових дій. Проаналізовано переваги використання робототехніки у процесі реабілітації та її вплив на покращення мобільності, якості життя та соціальної інтеграції військових. Висвітлено інноваційні методи та програмне забезпечення, що сприяють оптимізації реабілітаційного процесу. Результати дослідження підкреслюють важливість використання робототехніки як ключового елементу у покращенні якості життя та соціальної адаптації військових з ампутаціями. Встановлено, що використання робототехніки у фізичній реабілітації військових з ампутаціями сприяє покращенню мобільності та функціональних можливостей пацієнтів. Зокрема, застосування робототехніки дозволяє збільшити ефективність терапевтичних процедур, зменшити тривалість реабілітаційного процесу та підвищити загальний рівень самостійності та якості життя військових з ампутаціями. Висновки. Сьогодні використання робототехніки у фізичній реабілітації військових з ампутаціями має велике значення для покращення їхнього життя та соціальної інтеграції, а також є важливим напрямком досліджень і розвитку медичної науки.

The paper set up a system structure of the coordination of the human motor control system in layered modularization. A module of object hybrid impedance controller (HIC) was designed for it to compensate the whole dynamics. The inner force controller and movement controller were designed by adopting the method of nonlinear dynamic decoupling and impedance controlling. Integrated controller of two-robot can be realized by combining those two controllers. It was shown in the experiment result that the two-robot coordination control system was control effect is satisfactory and met the design requirement.

Controlling a mobile robot using conventional control devices requires skill and experience, and is not intuitive, especially in complex environments. For human-mobile robot cooperation, the direct-teaching method with impedance control has been used most frequently in complex environments. This thesis proposes a new direct-teaching method for a mobile robot utilizing variable impedance control. This includes analysis of user intention, which is changed by force and moment. A fuzzy inference technique is proposed in this thesis for identification of user intension. The direct teaching of a mobile robot based on variable impedance control through fuzzy inference is experimentally verified by comparing its efficiency to that of the conventional impedance control-based direct teaching of a mobile robot. Experimental data, such as the total time consumed, path error time, and the total energy used by the user, were recorded. The results showed that the efficiency of variable impedance control was increased.

Assist-as-needed (AAN) algorithms for the control of lower extremity rehabilitation robots can promote active participation of patients during training while adapting to their individual performances and impairments. The implementation of such controllers requires the adaptation of a control parameter (often the robot impedance) based on a performance (or error) metric. The choice of how an adaptive impedance controller is formulated implies different challenges and possibilities for controlling the patient's leg movement. In this paper, we analyze the characteristics and limitations of controllers defined in two commonly used formulations: joint and end-point space, exploring especially the implementation of an AAN algorithm. We propose then, as a proof-of-concept, an AAN impedance controller that combines the strengths of working in both spaces: a hybrid joint/end-point impedance controller. This approach gives the possibility to adapt the end-point stiffness in magnitude and direction in order to provide a support that targets the kinematic deviations of the end-point with the appropriate force vector. This controller was implemented on a two-link rehabilitation robot for gait training—the Lokomat®Pro V5 (Hocoma AG, Switzerland) and tested on 5 able-bodied subjects and 1 subject with Spinal Cord Injury. Our experiments show that the hybrid controller is a feasible approach for exoskeleton devices and that it could exploit the benefits of the end-point controller in shaping a desired end-point stiffness and those of the joint controller to promote the correct angular changes in the trajectories of the joints. The adaptation algorithm is able to adapt the end-point stiffness based on the subject's performance in different gait phases, i.e., the robot can render a higher stiffness selectively in the direction and gait phases where the subjects perform with larger kinematic errors. The proposed approach can potentially be generalized to other robotic applications for rehabilitation or assistive purposes.

Composite performance of variable stiffness actuator for exoskeleton administrated via impedance control and disturbance observer