# Three-Dimensional Assessment of Upper Limb Proprioception via a Wearable Exoskeleton
## 2 Materials and Methods  
### Subjects and Experimental Setup  
A group of eighteen healthy and right-handed subjects (8 females and 10 males, 27.94 \(\pm\) 3.83 (mean \(\pm\) std) years old, range: 22-33 years) took part in this study. In the group, there was no significant difference in the age distribution between males and females. For all the subjects, we evaluated the handedness through the Edinburgh Handedness Questionnaire [40] (Laterality score (LS) = 81.89 \(\pm\) 13.07 (mean \(\pm\) std), right-handed if LS \(>\) 60). All participants provided their informed consent. The experimental protocol was approved by the Heidelberg University Institutional Review Board (S-287/2020), and the study was conducted in accordance with the ethical standards of the Declaration of Helsinki. Experiments were carried out at the Aries Lab (Assistive Robotics and Interactive Exosuits) of the University of Heidelberg, Germany. Subjects self-reported no evidence or known history of neurological diseases and exhibited a normal joint range of motion and muscle strength. The experimental design involved a task where subjects worn the bimanual Arm Light Exoskeleton Rehab Station ALEx-RS [38; 39], shown in Figure 1A. An initial phase was run before starting the experiment to allow participants to familiarize with the device and its dynamics. Subjects wore a mask over their eyes to occlude vision during the whole experiment. The device consists of two identical robotic exoskeletons with 6-DoFs for each side. Four DoFs are sensorized and actuated: shoulder abduction/adduction (AA\({}_{\text{Shoulder}}\)), shoulder pronation/supination (PS\({}_{\text{Shoulder}}\)), shoulder flexion/extension (FE\({}_{\text{Shoulder}}\)) and elbow flexion/extension (FE\({}_{\text{Elbow}}\)); the other two DoFs are only sensorized: wrist pronation/supination (PS\({}_{\text{Wrist}}\)) and wrist flexion/extension (FE\({}_{\text{Wrist}}\)). The latter was blocked during the experiment to avoid uncontrolled movements. The range of motion (ROM) of each exoskeleton can approximately cover 92% of the upper limb workspace: the system is powered by a tendon-driven transmission system with low inertia and makes the overall structure highly transparent. Four brushless motors provided maximum torque values of 35 Nm for both AA\({}_{\text{Shoulder}}\) and PS\({}_{\text{Shoulder}}\), 25 Nm for FE\({}_{\text{Shoulder}}\), and 20 Nm for FE\({}_{\text{Elbow}}\). The controller of the device includes the possibility to use the workstation in 3 modalities: (i) \"passive\", in which the subject individually moves her/his arms in a back driveable dynamic mode; (ii) \"assistive\", in which the robot drives the upper limbs during the task execution; and (iii) \"assisted-when-needed\", in which the robot guides the user's arm when she/he is not able to initiate movements exceeding a time threshold. In all of the three modalities, the exoskeletons provide gravity and friction compensation, and the inertia is mostly cancelled by an inverse dynamic model running during operation and perceiving the user's motion by the absorbed currents from the motors. In the framework of the current contribution, an impedance control has been adopted to allow the user to actively match the imposed target and being passively guided by the robot during the target presentation as described in the following section. Figure 1: **(A)** Bimanual ALEx-RS device. (**B**) Block sequence presented to the participants during the ipsilateral joint position matching (JPM) task. (**C**) Task representation: participants sat on the workstation chair wearing one of the robotic exoskeletons, according to the tested body side. They were requested to grasp a pressure-sensitive handle of the contralateral exoskeleton (non-tested side). On the top left is illustrated the single joint (SJ) condition for the AA\({}_{\text{Shoulder}}\), on the top right for the FE\({}_{\text{Shoulder}}\), on the bottom left for the FE\({}_{\text{Elbow}}\). On the bottom right is illustrated the multi-joint (MJ) condition.