# NURSE-2 DoF Device for Arm Motion Guidance: Kinematic, Dynamic, and FEM Analysis
###### Abstract
This device has a bulky frame structure that is difficult to transport. In addition, the exoskeleton structure is hard to wear. Commercial devices are currently also available for upper limb exercises. In [13, 14], a commercial exoskeleton with ergonomically actuated shoulder is presented. However, it has voluminous bars and frame. In addition, it is hard to wear and it is expensive. In [15, 16], a popular device that consists of a visual interface and a robotic arm to guide the patient's arm along desired paths is presented. A five-bar mechanism is used to drive the robotic arm by two motors, which execute horizontal motions. In addition, a modular end-effector assists the wrist joint movements. However, the device is very complex and difficult to operate and requires well-trained staff to guarantee safe operations. Moreover, the device is expensive, heavyweight and it has a very tiny workspace for the exercises. In [17], a sophisticated commercial device based on the exoskeleton in [13, 14] as described in [18] is presented. The exoskeleton has six degrees of freedom to perform 3D motions and a graphical interface for virtual interaction. However, this exoskeleton presents the similar disadvantages of the exoskeleton in [13, 14]--a bulky frame, difficulty to wear, and costly. ReoGo is a commercial and portable robotic arm [19] that has a mechanism similar to a joystick. ReoGo performs two-or three-dimensional movements and it also has an interface for virtual interaction. The disadvantage of ReoGo is its small workspace. NeReBot is another device for arm therapy [20]. NeRebot is a cable-suspended device of three DoF with three cables whose end-effector moves inside a spatial working space. The robot cables are driven by three electric motors. The cables are connected to the patient's upper limb by using an arm support whose end-effector moves inside a spatial working space. The structure to support the cables can be adjusted manually. The NeReBot performs repetitive passive movements of the upper limb and it can be used by having the user in a chair or a bed. However, NeRebot is heavy and presents some disadvantages [21]--it is bulky and some horizontal movements of the upper limb cannot be performed properly. Rehabilitation centers often use the skateboard instrument to assist the training exercises for the upper limb [22]. The skateboard consists of a wheel board that enables horizontal movement. Using the sketboard, a therapist guides the movement of the patient's arm and the patient does the movements by himself. The skateboard is an affordable system, but usually does not have a regulated movement. In [23], a portable device for arm therapy similar to a skateboard is proposed. The mechanism consists of a mobile platform with three spherical wheels. The platform is attached to the forearm and it can perform movements in a horizontal plane. The device has an optical tracking system that is composed of two optical mouse sensors. However, since the platform is not attached to a fixed frame the patient's reaction can easily alter the reading of the mechanism positions. As described in the above paragraphs, the existing devices has several issues. Table 1 shows a summary of advantageous and disadvantageous features of the referenced devices. Regarding exoskeletons and semi-exoskeletons in [10; 11; 12; 13; 14; 17; 18], despite offering a large workspace they present bulky frames that hinder its transport and its building. Most of them use of bulky links that must be moved by the motors requiring greater torque than if light links. In addition, the exoskeletons are difficult to wear since they should surround the patient's arm as if it were a sleeve. Moreover, the joint axes of exoskeletons should be aligned with the anatomical axes of the human arm and it is hard to get it considering that the human arm sizes are different for each subject. In addition, it should be mechanically reconfigured for right and left human arm.