# NURSE-2 DoF Device for Arm Motion Guidance: Kinematic, Dynamic, and FEM Analysis
###### Abstract  
Patients with neurological or orthopedic lesions require assistance during therapies with repetitive movements. NURSE (cassiNo-qUeretaro uppeR-limb aSistive dEvice) is an arm movement aid device for both right- and left-upper limb. The device has a big workspace to conduct physical therapy or training on individuals including kids and elderly individuals, of any age and size. This paper describes the mechanism design of NURSE and presents a numerical procedure for testing the mechanism feasibility that includes a kinematic, dynamic, and FEM (Finite Element Method) analysis. The kinematic demonstrated that a big workspace is available in the device to reproduce therapeutic movements. The dynamic analysis shows that commercial motors for low power consumption can achieve the needed displacement, acceleration, speed, and torque. Finite Element Method showed that the mechanism can afford the upper limb weight with light-bars for a tiny design. This work has led to the construction of a NURSE prototype with a light structure of 2.6 kg fitting into a box of 35 \(\times\) 45 \(\times\) 30 cm. The latter facilitates portability as well as rehabilitation at home with a proper follow-up. The prototype presented a repeatability of \(\pm\)1.3 cm that has been considered satisfactory for a device having components manufactured with 3D rapid prototyping technology. m 20202019 March 202021 March 202017 February 20202019 March 20202019 March 20202017 February 20202019 March 20202019 March 20202019 March 20202019 March 20202019 March 20202019 March 20202019 March 20202019 March 202020201  
has four guides that restrict the motion of the end-effector in a vertical line, a horizontal line and two 45-degree diagonal rows. The path movements include the shoulder and the elbow. Nevertheless, since mechanism paths are restricted by four guides that limit the end effector along right lines, it is impossible for the mechanism to do other exercises. Moreover, without the flexibility required to adapt the practice/therapy to individual needs all patients should carry out the same trajectories. In addition, the patient response can modify the tension of the wires because the unit has a cable-driven system. Another portable device is presented in [9]. The device is composed by a base plate, hydraulic damper, restrictor arm, actuator arm, elbow cup, and hand grip. The device can assist the internal and external rotations of both right and left shoulders. Using the device, the arm should be attached to the device so that the elbow is located in a fixed position and the hand should grasp a handle. The device can get a horizontal or inclined position. However, the device can only perform one exercise and it can only assist the shoulder joint but not the elbow. Although existing systems have a large workspace, they are very difficult to carry, build, and wear. In [10], the authors proposed a planar three DoF (degrees of freedom) exoskeleton robot that assists horizontal motion for shoulder, elbow, and wrist. The exoskeleton is controlled by a cable-drive system. The user's arm is located on the top of the robot structure. The distances between the axes can be adjusted for each subject. Nevertheless, since the apparatus requires a voluminous framework structure, transportation and construction is hard. The biomedical robot is furthermore adjustable only for the right upper limb, and the design has problems in aligning the mechanism joints with the upper limb joints. An exoskeleton powered by a cable is presented in [11]. However, the exoskeleton is hard to dress because its exoskeleton structure surrounds the upper limb. However, it offers additional exercises regarding the exoskeleton in [10]. Another example is presented in [12], where a biomedical device is proposed for a robotized rehabilitation for a human upper limb. The biomedical device is an exoskeleton type that is principally composed by two rigid rods that are associable with the forearm and the upper arm by joints with four degrees of freedom.