A bio-cooperative approach for upper limb robot-aided rehabilitation

The design of patient-tailored rehabilitative protocols has a crucial role both in the clinical and research fields. Moreover, the inclusion of the patient in the robot control loop and a control strategy adaptable to the user's requirements are expected to significantly improve functional recovery in robot-aided rehabilitation. Ambition of this thesis is to design and develop of a bio-cooperative platform for upper limb robot-aided rehabilitation based on human-in-the-loop approach. The proposed platform is composed of an end-effector robot arm, a purposely developed arm-weight support of patient limb and a multimodal interface to constantly monitor patient status. It is equipped with sensors that allow recording kinematic, kinetic and physiological data both during the evaluation phase of the patient and during the rehabilitation treatment. It is capable of adapting therapy characteristics to specific patient needs, thanks to biomechanical and physiological measurements, and thus closing the subject in the control loop. The level of arm-weight support and the level of the assistance provided by the end-effector robot are varied on the basis of muscular fatigue and biomechanical indicators. An assistance-asneeded approach is applied to provide the appropriate amount of assistance. An overview of the validated tools for patient evaluation, used both in the clinical setting and in research, was presented. In addition, sensory systems, such as position/force, magnetoinertial (M-IMU) and electromyographic (EMG) sensors, and indicators extracted from these signals, presented in the state-of-the-art, were analyzed. Among these, muscular hand synergies in chronic stroke patients have been investigated in combination with robotaided rehabilitation. The results show a good similarity of muscle patterns between the affected and the healthy hand of the same subject. Furthermore, following the robot-mediated rehabilitation, the muscular synergies of the affected hand they tend to look like those of the healthy limb. Muscle synergies can also be a useful tool for assessing the patient's status, especially in patients with mild and moderate impairment. The platform and the adopted control strategy have been tested on 8 healthy subjects performing point-to-point 3D movements. The trajectory executed by the forearm support has been monitored to assess the performance of the chosen control approach. Moreover, a questionnaire based on the Likert rating scale has been submitted to the subjects to evaluate the overall platform. Preliminary results showed that the proposed control algorithm allowed to follow the arm movement in 3D space with a reduced position error. Moreover the subjects felt their arm completely supported, free to move in any direction of the space and judged the platform easy to use. The proposed bio-cooperative approach has been experimentally validated on 10 healthy subjects; they performed 3D point-to-point tasks in two different conditions, i.e., with and without assistance-as-needed. The results have demonstrated the capability of the proposed system to properly adapt to real needs of the patients. Moreover, the provided assistance was shown to reduce the muscular fatigue without negatively influencing motion execution. Repetitive and intensive exercises are the main features of robot-aided rehabilitation, but they may expose patients to inappropriate and unsafe postures. The introduction of a sensory feedback can help the subject to perform the rehabilitation task with an ergonomic posture. A preliminary evaluation on eight healthy subjects shows that the use of the proposed platform allowed subjects to execute highly controlled movements while maintaining an ergonomic posture able to limit the trunk compensatory movements during reaching. The introduction of visual and vibrotactile feedback in the proposed robotic platform for upper limb rehabilitation has been proposed to ensure ergonomic posture during rehabilitation. The two feedback modalities have been used to provide information about incorrect neck and trunk posture. Ten healthy subjects have been involved in this study. Each of them performed 3D reaching movements with the aid of the robotic platform in three different conditions, i.e. without feedback, with visual feedback and with vibrotactile feedback, and a comparative analysis has been carried out to evaluate feedback effectiveness, acceptance and performance. Experimental results show that in case of no feedback the subjects reach and maintain configurations that can lead to incorrect neck and trunk configurations and therefore, if repeated, to musculoskeletal disorders. Conversely, with visual or vibrotactile feedback, the subjects tend to correct inappropriate posture with both trunk and head during task performing. The proposed bio-cooperative platform is currently adopted in a clinical trial on 10 workers suffering from humerus fracture and subjects in aftermath of surgical repair of rotator cuff injury. The objective is to verify the efficacy of the proposed platform for robot-aided rehabilitation of the upper limb in workers affected by musculoskeletal pathologies.