Rehab-DUET: Bimanual Rehabilitation System for Distal Upper Extremity Therapy

Neurological injuries are the leading cause of serious, long-term disability in developed countries according to statistics by World Health Organization. Each year about 15 million people suffer a stroke, the most common neurological injury, causing loss of their independence and significant decrease of their welfare. Studies have shown that physical rehabilitation therapy is responsible for most of the recovery experienced by patients with disabilities secondary to neurological injuries, and the therapies are more effective when they are task specific, intense, repetitive, and allow for active involvement of patients. Using robotic devices in repetitive and physically involved rehabilitation exercises helps eliminate the physical burden of movement therapy for the therapists, and enables safe and versatile training with increased intensity. Robotic devices allow quantitative measurements of patient progress while enforcing, measuring, and evaluating patient movements, and with the addition of virtual environments and haptic feedback, they can be used to realize new treatment protocols. Therefore, these devices not only help increase the reliability, accuracy, and effectiveness of traditional physical rehabilitation therapies, but also help extend their applicability beyond the boundaries of clinics, realizing “hospitals without borders”.

Despite the benefits of the robotic technologies on rehabilitation, human involvement continues to be vital in rehabilitation systems for high level decision making. Therapies require supervision of the therapists as well as their active guidance and expertise. On the other hand, the proper amount of assistance to be provided while completing a therapeutic task requiring limb coordination may be best judged by the patients themselves. Furthermore, social communication and human interaction in the form of competition or collaboration are known to increase patient motivation.

Rehab-DUET project aims at developing a powered, teleoperated, exoskeleton-based rehabilitation system to assist physical therapy of forearm and wrist. The system is based on a multi-lateral control architecture so that that human experience and judgment can be included in a robot assisted therapy session. The project involves a) design and manufacturing of powered exoskeletons to assist forearm and wrist rotations, b) derivation and implementation of bilateral control techniques with stability guarantees, c) synthesis of novel bilateral and teleoperated assistance methods (such as self-induced therapy of patients through use of their healthy arms or therapies that allow patients to pick their preferred pace for the task while also ensuring their active participation), and d) design of human subject experiments to test feasibility and ergonomy of the developed assistance methodologies.

At the end of the project a 4 degrees of freedom (DoF) powered exoskeleton is designed for rehabilitation of forearm and wrist rotations as shown in Figure 1. The kinematics of the device has been selected as a hybrid 3RPS-R mechanism to match human joint movements, while multi-criteria design optimization has been conducted for the dimensional synthesis of the mechanism to simultaneously optimize actuator utilization and workspace volume index of the device. Singularities of hybrid kinematics of the exoskeleton have been studied using Grassmann line geometry and the largest singularity free workspace of the device has been characterized and implemented. Two identical exoskeletons have been manufactured and experiments have been conducted to characterize their performance.

Figure 1: 4 DoF powered exoskeleton with hybrid kinematics designed for rehabilitation of forearm and wrist rotations

Local control of forearm-wrist exoskeletons for multi DoF orientating tasks has been implemented using passive velocity field control (PVFC). PVFC is of particular interest, since this method emphasizes coordination and synchronization between various DoF, while letting the speed of the task be decoupled from them. Hence, patients are allowed to proceed with their preferred pace, while assistance can still be provided as determined by the therapist. Furthermore, this method not only minimizes the orientation error but also does so by rendering the closed loop system passive with respect to externally applied forces. To ensure active involvement of patients throughout the robotic therapy sessions, systematic approaches have been developed to prevent slacking – continuous decrease in the levels of muscle activation during repetitive motions as the movement error becomes small– a fundamental property of the human motor control. The novel slacking prevention scheme is based on the PVFC framework and enables seamless on-line modification of the task difficulty, speed of orientating task and the level of assistance, while preserving passivity of the system with respect to external forces. Ensuring coupled stability of the overall robot patient system is a novel property this slacking prevention scheme that cannot be assured with any of the other existing methods.

The two forearm-wrist exoskeletons have been adapted as parts of a tele-rehabilitation system that is controlled through a novel method in the rehabilitation domain as depicted in Figure 2. In particular, the multi-lateral shared control concept has been implemented for rehabilitation, in which different control authority can be assigned to each robot. With this controller in place, the tele-rehabilitation system is capable of providing passive, assistive, resistive, and bilateral therapy modes and features virtual reality integration and force-feedback. In one of the control modes the system gives the control over external mechanical assistance of forearm and wrist movements to the patients themselves, to allow users to practice “self-induced therapy” through use of their healthy arms. For patients with an injury that afflicts an arm, the system allows them to “retain” the centers of brain and spinal cord dedicated to the arm by using their intact arm. In this manner, the patients can be established as active participants in the rehabilitation process. In another control mode, the system gives the control over external mechanical assistance of forearm and wrist movements to the therapist. In this case, the therapist can use his/her expertise to assist/resist the patient as deemed proper. This control mode can also be used for “remote assessment” of the patient through teleoperated interaction with the therapist. In the third control mode, two patients can interact with the same virtual dynamic environment. This control mode allows “group therapy” and can increase patient motivation through competition or collaboration.

Figure 2: Forearm-wrist exoskeletons forming a tele-rehabilitation system with multi-lateral shared control

The system can implement all of the assistance modes proposed to date, as well as implementing the above listed novel bimanual, bilateral assistance schemes. Facilitating active participation of patients and self-teleoperated modes, the system is expected to not only help expedite recovery process and increase treatment effectiveness, but also enable personalization of care, offering new opportunities in health and disease management. Furthermore, the system renders home based group therapy, remote assessment of patient progress, and remote diagnostics possible. Finally, as is the case with all robotic therapy devices, the system allows patients to be closely monitored and lets their data be correlated with patient databases.

The feasibility and ergonomy of the system as well as the proposed therapy modes have been tested with healthy volunteers and the system has been evaluated as ready and appropriate for clinical trials. Clinical trials are planned with several healthcare institutions and hospitals within the near future.

The developed rehabilitation system features many novelties in terms of its optimized mechanical design, unique local and tele-operation controllers that enable novel therapy modes. The proposed methodologies promise significant advantages over conventional approaches and have the potential to substantially impact progress towards radical improvements to the quality and effectiveness of physical therapy. Advancement of robotic rehabilitation promises not only help offset the detrimental economic impact of the ageing population in Europe, by reducing physical therapy costs and helping regain disability related labor loses, but can also improve welfare of millions of people suffering from disabilities secondary to neurological problems.